What should I do for iTunes before reinstall win7? I have backuped my apps, books and songs in iTunes, but how about the data in apps, such as the saved angry birds' progress, the pdf files in adobe reader and so on?
You can save the whole iTunes folder(it should be at ../Music/iTunes directory) and just put it back after you reinstall iTunes on your new Windows system (new iTunes installation will put it's new "blank" folder in /Music, just replace with your backup copy).

By doing so iDevices will recognise your library as the one they had synced with before and will continue to sync with it like nothing happened, hence keeping all the saves on the devices.