Bare minimum, a fixed gear rear wheel. If you're lucky, you'll be able to remove chain rings from the crankset that comes on it (since you only want one.) OR, if there's, say, two chain rings, you can just put the chain on the smaller one and use the larger chain ring as a guard. And no, you won't need a better frame, unless the one you buy is broken or something, but then again, you wouldn't buy that in the first place. Basically, if you want a small project and like the look of an older bike, convert one yourself. It's MUCH more rewarding than just going out and buying a brand new fixie. That being said, I think new fixie frames look stupid, so my answer is obviously biased. Also, if you build the bike yourself, you end up learning quite a bit about it, which is great since you wont have to take in into your LBS to fix it (if a small problem occurs.) If you don't like the older look, you can also strip, prime, and paint the bike whatever color you want.