if you're thinking of converting, you might be better off finding an old steel bike at a thrift store and buying a fixed rear wheel on ebay.
a great place to start learning about fixed-gear conversions is sheldon brown's site;
http://sheldonbrown.com/fixed-conversion.html
there're also a bunch of helpful folks on these boards; most of your questions have probably already been answered by one of 'em at one time or another, so go nuts searching old threads.
if you can't find an answer start a new thread.
good luck and welcome!