There is this guy who volunteers at the Bicycle Commuter's shop (Bikeworks) who knows a little bit about fixed gear conversions since he's built way more than 6 of them and owns 4 himself.
That would also be me.
I'm at the shop Monday and Wednesday nights and usually pop in on Saturdays to see if the weekend crew needs any help.
PM me if you want to know more about fixed gear conversions, Bikeworks, or the Commuter's society.