I have read through this entire thread and I think I have to add my two cents here as well.
I'm not really gonna touch the 'fact' that the Minbari whooped the EA fleets and sufferred relatively little losses in comparison. That has pretty much been established, and I'll leave it to others to argue specific casualty figures.
Now, let's get into the juicy part, that of planetary assaults. For this I'll start at the top of the equation.
Securing the Beach Head: This was probably the least painful part of the operation for the Minbari as they would only need to gain space superiority at the area of insertion. The Minbari are most definitely capable of this phase. The technology gap would be most apparent here with their fleets able to bring their full power to bear. Minbari losses at this point would be little to none.
Insertion: Here is where we see the assault forces disembark from their transport vessels and begin descent through the atmosphere. Their entry into the atmosphere here is going to leave them vulnerable and very, very detectable to any Air-Defense assets. The heat corona from their entry will probably completely nulligy the effects of their jammers allowing ground based weaponry, atmospheric craft, and all other battlefied systems to engage them with great proficiency. This will be a very painful but probably very shortlived strike as the Minbari fleet vessels begin targeting the Earther's Air-Defense assets. Losses could very well be staggering at this point, dependent on the ability of the ground commander to concentrate his assets at the point of insertion.
-Note to those thinking that it would be easy for the Minbari to detect and destroy said Air-Defense systems before insertion; this is nowhere as easy as it sounds if the defender leaves his active systems off until he needs to engage his radar. As well, the defender can minimize the effect of orbital fire by setting his Early Warning Radars up to feed information to his weapon systems. This way those radar sites will be targeted instead of the Air-Defense systems.
Securing the Beach: No Marine is ever more vulnerable then when he is disembarking his boat while trying to find cover, locate the enemy, and keep track of his fellows, all at the same time. Expect even more casualties against the Minbari here as the EA Commander is now able to bring to bear several different combat systems. (Remember "Saving Private Ryan" when they were storming the beach) Artillery will come into its own here, as I'm sure the targeting and delivery systems have progressed quite a bit in the two centuries of development between present day and the B5 timeline. As well you may see the employment of Armor and Mechanized Infantry to add direct fires to the mix, and, if available, you might even see the use of CAS (Close Air Support).
The Minbari fleet will be able to bring to bear some of its weaponry once they have located the source of the artillery, but it's effectiveness would have to depend on the artillery's capabity to either displace after firing or even fire on the move. This will help to lessen the effects of the Minbari counterbattery. The fleet will be hard pressed to help the individual Minbari soldier as orbital bombardment on a location your troops are trying to occupy just doesn't sound like a good idea. So, depending on the level of commitment to the 'beach', Minbari losses here could be high.
-Note, within this phase all fire will be directed by someone on ground with the old MK-1 EYEBALL. It never hurts to have a Forward Observer directing the artillery while a Forward Air Controller directs the aircraft. All I gotta say is that is sucks to be a Minbari in the kill sack.
Exploitaion: Here is where we see the Minbari troopers begin to push forward towards their objectives once the 'beach' has been cleared of enemy opposition. The level of resistance at this point depends on how layered a defense the Earth Commander was able to establish. Whether or not he was able to emplace ambush sites along the routes of attack the Minbari will use and if he decided to leave a flanking force in place to strike once the Minbari moved past. Here is where the Earthforce numbers will become telling. However, too much movement of ground troops will more than likely be detected, and large formations can expect to be attacked by either Nials, armor, or even orbital fire. Stealth and subtlety will be a key to defending against the Minbari advance. So losses for the Minbari here will almost completely depend on the millions of variables that are inherent in an operation like this. However, they will probably be on the low end as the Minbari commander will now be able to concentrate his forces and establish a strong presence in his area.
Attack on Objective: This is gonna be the meatgrinder. It's where the Minbari are going to be attacking the main defensive position held by the Earthforce. It will more than likely be hardened to protect against orbital bombardment and will need to be cleaned out by the infantry. Booby traps and bottle necks will be the name of the game for the defenders while speed of penetration and bloody persistance will be the aim of the attackers. Urban warfare at its ugliest here folks. The Minbari will have an advantage here becuase of their generally increased strength and speed, but that only takes you so far against a PPG, autoshotgun, or whatever crew served weapon happens to be spitting death at you. What will get them through the day will be their individual level of training imparted on each Minbari soldier. Casualties on both sides will be high here.
Guerilla Operations/Mopup: This is what you are going to see once the focal point of the Earthforce defense has been neutralized. What will make this even worse for the Minbari is the feeling among the local population that they are going to be exterminated. So every single able-bodied human is going to go down fighting if they can. They may not take a lot of Minbari with them, but they will certainly try.
Here are some other things to pay attention to when you are talking about Earth vs Minbari ground combat.
Sensors: They may have us beat their too, but it is still going to be a hell of a lot harder to pick targets out from orbit when you have to deal with weather conditions as well as ground clutter. Now, once something begins to emit some clear signal (ie. radio, strong power, etc.) it will be a lot easier to pick out of the woodwork. Unless of course some smart cookie placed it in an area where that kind of reading is present in large amounts.
Experience vs Training: Yes, the Minbari have a crapload more training on the individual soldier, but (and it was stated earlier) the Earthforce has a tradition of practical experience that goes back thousands of years. Most recently the ground campaigns against the Dilgar which give the leaders a central core of knowledge that is immensely valuable. Earth forces are trained to fight an 'amphibious' battle if you will. They are meant to be deployed from space to ground and as a result they know how to fight against it.
Technology Gap: You don't have to have the biggest stick in the yard to bash someone's head in. I know I'd certainly like to have the shiniest new weapon to defend myself with, but hey, there are ways in which you can limit the effectiveness of someone's technology, and I am fairly certain that the GROPOs in Earthforce quickly came up with ways to lessen the Minbari advantages.
OK, OK, I'm all done now. So let me know what exceptions you have to this, and we'll hash 'em out.