if you sync to your PC it will clear everything off of your buddies.
However, once you sync all of your stuff onto it you can ask him to download those 2-3 apps onto it again for free.
under settings on the ipad go to the app store settings. in here you can log out out of your account and have him log in with his to download the apps agian. after that go back into settings and log back into your itunes account. your ipad will then be synced to your PC and still have those 2-3 apps of your friends and they will stay there after future syncs with your PC.