Did you backup all your documents and data first? Normally your user profile contains a Music folder which in turn holds the iTunes folder. All the important details of your library are in there, with the media below in a folder called iTunes Media. If you lose this information and then connect your device to an empty iTunes library it will want to clean it out the device and start over.
You should be able to recover the media with the tips in this post from forum regular Zevoneer but I'm not sure what the implications are for your application settings. You can probably transfer your purchases into a newly authorised library, backup the device, recover any other media using third party tools, then restore the device from the backup. That might switch the assocation of the device to the new machine but I couldn't say for sure.