This subject came up a week or so ago. I haven't tried it yet, but it was suggested to use i-funbox, found here:
http://www.i-funbox.com/
You should be able to copy iTunes files(your music/videos) to your PC.
See the thread here:
http://www.everythingicafe.com/forum...ing-57014.html
Edit: Apple sees your computer as a separate machine(since you wiped it clean). If it makes you feel better to see only 1 authorized there is a way to unauthorize all computers in iTunes. Then start over on your 'new' machine, you won't have to change your account info.