Wikipedia page for more basics.
I really enjoyed reading about this setting; although sadly I was never able to get a game up off the ground. There were some fundamental flaws in rules at the time, and if I remember correctly, D&Ders either loved it or hated it. I was surrounded by gamers who hated it, thus I never played it for more than one or two sessions.
Fortunately this morning I crawled out from under my rock and discovered Birthright is alive and well! There's a very vibrant and growing community tucked away on the net that apparently even once had the tacit approval of WotC to publish a d20 update to the Birthright setting. I also found that there is an effort to convert/update the Birthright rules to 4th Edition. Of course, some major changes to 4E would be needed for this to work, but it should be interesting if it ever gets off the ground.
Have any of you played Birthright beyond a few sessions? What was your impressions of this 'version' of D&D?