Also, to get an EASTERN fighting class, you cannot choose a second tier fighters guild class, ie, Marauder or knight. Its not clearly stated generally, but Eastern fighting classes require the following: you to be a tier 1 fighter, not to choose a tier 2 fighters guild class, and the quests mentioned above by swcarter.
Also note that you can choose to be an Eastern fighter and take on the sisterhood classes. Nothing prevents this.
Also, note that the Budoka/Ninja Lord classes require taking on the rogue class first, so it seems you can take on 2 tier 2 eastern classes, one fighting, one rogue. If haven't tried this myself though.
GameBanshee just put up a really need progression sheet for class advancement here:
http://www.gamebanshee.com/dungeonlords/classes.php