You're going to want to do a lot of reading of the forum; all the answers are in people's various threads about homebuilt chaindrives and such. It'll get you experience vicariously about all the problems you may encounter, too.
Look for Bottom Bracket (BB) drive, Chain Drive, Stokemonkey (SM), Cyclone, etc., for a few search terms to get you started.
If you look at my DayGlo Avenger and CrazyBike2 threads, you'll see a few possible methods and problems. REdiculous has a treadmill motor build thread. Many others are documented in quite a lot of detail here on ES, too, but you'll want to read around (mostly in this subforum) to find out the questions you will really need answered, once you get far enough to ask them.