Can I upgrade my 2008 iMac Motherboard and processor?

Hi all,
I picked up a low end 2008 iMac for $200. I was wondering if I could swap out the motherboard and processor for a later model's or possibly a 3rd party motherboard/processor? I'm interested in getting Target Display Mode to work and then use my Mac like a KVM switch in my lab. The Target Display Mode feature isn't available until later model Mac's. Any guides out there on doing something like this? Is there a compatibility list I could peek at? Is what I'm attempting even possible?

Thanks in advance!