How do I sync my apps onto the computer?

I got an iPod touch and bought a lot of apps and I wanted to sync them on the computer, just in case it gets stolen, I can sync all my apps back to my iPod touch. But it had a virus and somebody fixed it but they reset the whole computer. So I want to sync them again, but it says "Erase and Sync"! I don't want to erase everything from my iPod! And I can't sync them back 'cause that guy erased everything from the computer! HELP!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!…