With regards to iTunes, assuming you have XP, you’ll need/want to backup one, possibly two folders.
The first is your “My Music” folder in “My Document” as that’s where your iTunes library database file stored - even if your main iTunes music folder (where your actual music files are downloaded/installed) is located elsewhere. If you do have your music folder located on the same drive, back that up as well.
Personally I’d recommend you put the actual Music folder on a separate HD and keep a current backup of the “Music” (Vista)/”My Music” (XP) folder in a safe place. I would also recommend backing up your actual music folder. Some useful info - when you do a Vista update/install, Vista will create a folder called “windows.old” and put your XP contents there. (backup anyway!!! just in case!) Once Vista is up and running you can go in that folder and copy/move contents as you wish, than either keep, or delete the folder through “Disk Cleanup”
Before upgrading to Vista I’d advise you to run the “Upgrade Advisor tool. This will point out any potential software/hardware problems when moving to Vista. You can get it here - Download details: Windows Vista Upgrade Advisor
, or if you already have a Vista disk, you can run the program from it.
I would also advise you look to see if your printers have vista compatible drivers
You’ll also probably want to check out this tutorial on installing Vista upgrade - Clean Install From Upgrade Vista
Hope this long winded explanation helps