This site should answer all your questions. It has information on all versions and, most importantly, a test to see which versions your PC can run.
http://www.microsoft.com/windows/products/windowsvista/buyorupgrade/upgradeadvisor.mspx
I know there are various versions available. How can I find difference in each version (e.g. Home, Business etc.) & help to decide which one I should go for?

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic