Assuming you have a Powerleap adapter, you should be able to use any 100MHz FSB FCPGA (not FCPGA2). AFAIK, that means you should be able to go up to a Celeron 1.0 or 1.1 (not 1A or 1.1A). You would want the ones with 128K of cache, not 256.
Don't take my word for it though.