http://sheldonbrown.com/fixed-conversion.html

Here is useful site for beginners. Please note that to turn your mtb into a SW33T FIXAY you will end up replacing the following parts with fixed/singlespeed specific parts

- rear wheel and hub
- crank

Most conversions will run you at least $100, assuming that your frame is compatible and that your parts are in good condition, which they are not.

In all, do more research, and find out what kind of bike you eventually want. There are too many project bikes where the owner had an old frame, wanted something completely different, spent an ungodly amount of money upgrading their old frame only to get a bike that will never meet their expectations.