For the most part, I would need to know some of the classes involved so that I could gauge my ideas from. But, here are a few "stock" choices for someone new to the world of Magnamund.
1) Visit
http://www.projectaon.org and familiarize youself with Lone Wolf's adventures in books 1-5. They are the best example of the overall feeling that should be encapsulated by a table top game. The series is epic, covers thousands upon thousands of miles of travel, and basically (if I am converting the game books to d20 properly) decribe a lvl 5-10 campaign. For the record, the Magnakai series should cover a campaign for lvs 11-20.
2) I'd suugest starting characters off at no higher than 3rd. Too much higher risks robbing the players of the enjoyment of gain choice abilities. But by third level, everyone has something to contribute to the party (magician of Dessi gets his Staff, etc)
For Kai Lords:
1) Have a few rumors circulating about the Book of the Magnakai falling into the hands of a Helghast. The players should have a hell of a time recovering the tome from a agent of the darklords who can shapechange. This idea bests works as a climax within an existing series of adventures.
2) A scouting party along the Durncrags goes horribly wrong when Giaks, Vordaks and Karran attack a group of Kai. Very few survive as they were badly outnumbered, and now the survivors are being taken to Kaag for the culinary pleasure of Darklord Zagrana. The story should be one of hopelessness, strife, and finally escape - possibly with some great piece of intelligence that later turns out to save lives, resources, etc.... This scenario best works as the entire body of an adventure.
For Buccaneers (and maybe even renegade Bor Gunners):
1) Have a pirate captian strongarm a ship from one of the Northern regions, prefferably one allied to Sommerlund. (The characters should be members of the crew - not command staff) The ship is then commisioned by Holmguard for a mission for the Crown, and the crew is told nothing of its manner. Later, the find out (somehow) that their cargo is either:
a) a very important member of Sommlending nobility
b) a prestigous Kai Lord or Brotherhood adept
c) or, for a great twist, a helghast masqarading as one of the above.
The pirates should want to ransom off the captive, or get the captive to somehow provide riches and treasures, and so forth. Now for the kicker - I would play this session as the entire body of an adventure, and take heavy cues from the film "Suicide Kings" starring Cristopher Walken (who manages to turn the table completely around on his kidnappers with a few simple observations and a few choice words) Or, you could take a slightly more suspensful take on things, and have the helghast entertaining its sick and twisted pleasures but making everyone think it was bound, but killing off one crew member a night....
For Brotherhood Adepts and Magicians of Dessi
1) Simply have rumors of the Moonstone crop up. That should get things off to a running start rather quickly. Maybe rumors says that some Cener Druids got a hold of it, or maybe the Nadziranim. Of course, they are wanting the goodly artifact destroyed. Perhaps they really don't have it and they have been fooled into thinking that they do by a third and largly unknown party....
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Just the first few ideas that came to mind while trying to get the thread back on track. Hope you enjoy.