this may or may not work (it's worked for me every time i've need it, for retrieving files from a HD)... get a $20 external enclosure case that connects via USB or Firewire, put the old HD in it (make sure the jumper on the old HD is set to Master), connect it to your PC... then drag & drop, or copy & paste (or whatever your method is) to retrieve the files.
then, with something like Partition Magic, formatting the old HD and making it a single empty partition/drive is a snap as well. (you can even do this while the old HD is in the external enclosure.)
i did this very same thing about 6 weeks ago.