How to have 2 different itunes accounts on 1 computer?

Me and my dad just recently got iphones. But we both already have account because we have ipods.except my account is on a different computer. Is there any way i can keep that account and the songs on that account and switch to my dads computer. I also dont want my dads songs and he probably doesnt want mine either. So i need a way to have 2 different itunes accounts on one computer and still keep the same music. Can you please help? (most of our songs were downloaded and not bought off of itunes)

You can't

Try creating a second windows log on account.

If you have a separate account from your father than all you do is log into iTunes on your dads computer with your log in info and then create a second media library for yourself. Then do a back up of your iPod to iTunes using your new media library as the back up folder. This will put your music on his computer, but keep it separate from his. Be sure to log out when your done so he doesn't use your account.