I've been offered a way to upgrade to Windows 7 and I was wondering what stuff I'd have to do before the upgrade? What sort of files do I need to back up?
Back up all your personal data before an upgrade. I'd personally opt for a fresh install though. If it's a laptop you may need to download a driver set...
Back up your stuff and do a clean install. When I upgraded to Win 7 I just backed up my music, pictures, videos and Steam games to an external HDD and then transferred them back over once it was done. Win 7 should detect your hardware and download all the relevant drivers and stuff for you, but it's best to have the drivers disk handy.