Originally Posted by macscac
What if I created a second user on vista. Logged into that and installed iTunes. Then would there be any chance of getting our info mixed up?
You dont need to do that but if it makes you feel safer then by all means. if you do that and you sync your buddy's phone, he will lose everything he has on it. Like I said before, if you make sure to disable automatic syncing in iTunes (go to Edit>Preferences then click Devices tab then make sure "Disable Automatic Syncing for iPods and iPhones" is checked) you can then plug in your buddy's phone and when it appears on the main screen in itunes click "update" it will only update his phone (DO NOT click restore). it will leave your info alone on your computer and it will leave all of his apps/settings/contacts etc. alone on his phone. you both walk away happy. after its updated, on the iPhone go to settings>store and make sure it doesnt have your iTunes account info in there and you're all set. if it does, just tap sign out.
EDIT: IF you do create a new user on your PC and install iTunes on that new user account, you STILL HAVE TO make sure to disable automatic syncing.