New to Xcode so I'm not really sure about this. Is Xcode backwards compatible with previous versions? If I set up a GIT server on a mac running Leopard and an older version of Xcode, can I pull codes, edit and commit those same codes with machines running Lion and Xcode 4.2?
XCode and GIT does not really have anything in common at all. XCode 4.0 and beyond supports version control through GIT, but you can still use whatever version control system you would like. As long as the GIT server is a normal GIT server, you can have XCode 4.2 commit changes to it.