For info on FETS, IRC a manufacturer, has allot of info on their web site.
http://www.irf.com
Check this site out for a speed controller primer.
http://homepages.which.net/~paul.hil...ntrollers.html
There are single chip speed controller chips that will work for small motors and stepper motors. They can all so drive FETS. The following link shows the hardware and software control of one of these chips.
http://kronosrobotics.com/an101/DAN101.shtml
Research to understand speed controls is OK, But as far as making one. Why reinvent the wheel when hobby RC car controllers are quit cheap. Learning how to use speed controllers and stepper drivers in control strategies may be a better place to focus your energies.