I had to reintsall windows 7. What do I need to do to resync my ipod witout erasing and resetting it?

HI.

I had to reinstall windows 7. My backup was only on my computer. So it's gone. Could someone tell me if it's possible for me to sync my ipod touch with the new windows install without resetting and erasing it? I found an article that said that you could transfer purchases from your ipod touch to your computer but it was unclear as far as what you needed to do with the authorization. It's the same computer. Just a new OS.

Thanks.