21c3 is not a pci id that belongs to nvidia. There are two 7600GS cards listed in the nvidia device_ids_oct08.txt, 0x02e1 (G73) and 0x392 (G70). Both are listed in this database.
Many entries on the net like this one:
03:00.0 VGA compatible controller : nVidia Corporation G70 [GeForce 7600 GS] [10de:0392] (rev a1)
: nVidia Corporation G73 [GeForce 7600 GS] [10de:02e1] (rev a2)
The id 21c3 most likely is a the vendor id or the pci id on the subsystem (card manufacturer)