Dell Optiplex GX240 Motherboard?

I have a Dell Optiplex GX240, the big desktop, not the small one. I bought a 2.8ghz 800mhz fsb 1MB cache processor. My PC supports 533mhz fsb. I want a new motherboard for the processor. Would any mobo fit in the case or do I need a specific motherboard. Also I have pc133 sdram in now and i would like to keep it. is it cheaper just to get a bare bones package or what? Any ideas would be helpful, thanks.