Gearing help?

I am have absolutly no clue how, or where to start.

Is there a real world mathmatical formula for properly gearing a car?

Any help, breakdown on how to get proper gear ratios and final drive will help out alot.

Also is there any site where I can find stock gear ratios and final drive numbers?

http://forums.forza.net/turn10_postst14758_Need-some-help-with-gearing-maffs.aspx