So I'm tearing down an old mountain bike to paint and simply build back up when the fixie itch just hit me. I already have to replace the crankset because the teeth are worn down like crazy. IF I replace the crankset and put on a flip-flop hub in the back, is that all I need to do to enter into the fixie world? I'd want to switch from the 26" rims to 700c rims for less resistence. If I'm going to do it, I want to ensure I'm doing it right. That's why I thought I'd call upon the bikesperts!!! Thanks guys/gals.

What kind of bike is it, does it have horizontal dropouts or vertical dropouts?

It has vertical dropouts.

Pictures will help. Some say you have to have horizontal, but if your verticals are at an angle and have some room to move the axle around, you may be able to adjust chain tension with them.

My conversion has 'vertical' drop outs and the chain tension can be adjusted perfectly.