The Insprion 531 is fully compatible with Windows 7. All the drivers come from Windows 7, if you got the 32bit route, so you don't have to worry about Vista drivers. If you go the 64bit route, only one device is not supported. The Away Mode device, but there is a solution for that and I can give it to you if you decide on going to 64ibit.
Upgrading is the easiest way, but doing a clean install is the best way. Unfortunately doing a clean install will mean you loose all your data and programs. So a backup of you personal data would be necessary and you would have to reinstall all your programs. I've done both and hands down a clean install of Windows 7 runs much better