Dual Quad-core Xeon Server for...gaming?

Hey guys, so my parents work at a pretty big IT company and they got connections so my dad picked up a server randomly for $100, and is bringing it home tomorrow. The specs of it, from what I gathered so far, I will update them when I actually get to check the specs on it.

CPU: 2x Xeon Quad-core Server CPUs (3.0GHz each)
Motherboard: Some dual-socket server motherboard.
RAM: ~8GB, maybe more, unknown speed server RAM.
Storage: 400GB total capacity with multiple 15,000RPM drives.
GPU: NONE!
NOTE: Its about two years old, so I'm assuming pretty recent parts, PCIe x16 2.0 slots, RAM 800MHz+, etc.

My dad says hes going to use it to virtualize couple of OSs for around the house. I see the chance to use it to do some PC gaming.

So obviously, I'm going to have to add a GPU onto that. One graphics card I can think of that I can get immediately is a Radeon HD4850 1GB. So based on these specs, how well would it do at gaming? I read around and heard that most games don't use more that 4 cores, so if I can make a virtualized OS with 4 cores and using most of the processing power of the GPU, could I possibly play some Black Ops from my laptop that doesn't quite cut it?

Thanks.