This Sheldon Brown page talks about fixed gear conversions.
Fixed Gear Conversions A decent 1980s bike is your best shot at this project. Research what the general frame size you will need and then scour Craigslist for a bike or frame. Post what you find here so we can tell you if the frame will work and is worth the effort.
This forum and road cycling forum can be rough at times but no one means any real harm. Stick around, read a lot, grow a thicker skin.