All you would have to do is point itunes 6 in the direction of wherever your song library is stored on the pc - uninstalling itunes 7 will not delete your mp3s (or AACs)
Sorry when I said library I meant the actual songs on the hard disk. If you reinstall itunes 6 and tell it where your music files are it will construct a new library file from scratch.
To wipe the ipod you need to do a factory reset which is one of the options in the ipod update software available from apple.