That doesn't mean anything. Most games only use one or two cores some like Skyrim and BF3 does make use of 3 or 4 cores. The point is that a single quad core CPU is more than enough for gaming. Adding a second CPU isn't going to do aything for you. Most games are more reliant on the GPU and that GPU is junk. It's two, almost three generations old and isn't go to handle games like the AMD 7000 series or Nvidia GTX 600 series GPU's.
some misinformation above ,,,,,for starters i personally own a dual socket 604 xeon setup clocked in at 3.8 ghz with hyperthreading and rockin not too old ati 6870 graphics with 2 250gb ssd in raid with pcie raid card and running windows 7 64bit with 8gb ddr2 400 and this plays all current games at very nice frame rates no lag no issues and stupid fast i can destroy many core 2 duo systems out there not all but quite a few , you would need a pretty high end core 2 duo to match the xeon setup, i can tell you is commercial grade stuff is way better then any mainstream provided you know how to pick your board...
As others have mentioned, games are not the native habitat for Xeon workstations, but your HP vw8200 does have some positives that could go a surprising amount of improvement >
1. You can add a second CPU, another Xeon 64-bit single core. As is mentioned here, most games- and even most applications, including some 3D CAD are single threaded. That single core Xeon is probably the cousin of the Pentium 4 like the P4 660 3.6GHz-they have the same speed, and those are hyperthreaded so they appear as dual core. the single core is a detriment, but made up for by having 2, the hyperthreading, and the high clock speed.
2. You can buy 2 of the fastest Socket 604 Xeons' -the 3.8Ghz for $15. or another 3.6GHz for $5-10 !
3. There are 8 RAM slots - it's DDR2-400 ECC -and you can buy 4 X 1GB for something like $30 to have 8GB.
4. The vw8200 has a 600W power supply so you could have a GPU that takes quite a bit of power- 150-200W
5. The vw8200 has a PCI Express X16 slot, which is the current one for fast gaming cards.
6. There are 2- PCI-X slots to which you could add a very fast SCSI disk controller.
A lot of single core computers in that era didn't have CPU fans, but especially if you add a 2nd and/or faster, look for a fan cooling solution- even it's case mounted and blows on the CPUs from the side. The ones for Pentium P4 might work.
I don't know for certain, but your vw8200 was probably a quite expensive, higher end computer new- and well constructed. I had a 1998 Dell T700R Pentium III 750MHz, single core with 768MB RAM and that cost over $2,000.
As for the ideal graphics card, I'd look at which ever Radeon (better value than GeForce) PCIe X16 with 1GB memory and DirectX 11 suits your budget as used on Ebay. Probably, a proportional card purchase would be about $50. Or, you might look at the 896MB GeForce GTX 260 for around $35-40. I recently bought an EGVA 1GB GDDR5 GeForce GT240 from Newegg for $30. that appears to be new.
You might find this can work quite well. In my view, it's fun to get the old crocks moving along- and for little money. Getting a 3.6GHz Xeon CPU for $8. is like magic!