Yeah just download and install the PSPI plug in in your plug-ins folder. Restart GIMP, and go to Filters/Photo shop Plug in Path Click on it and a dialog like the GIMP path dialog will come up.Point GIMP to your 8bf's, or folders containing them using that dialog.
Restart GIMP...and there are your plug-ins.
I am not sure if photo shop key 3 will work thru GIMP though.Being a separate program plug in like alien it might. Test it and see. =)