Get a MSI K7D and just use dual XP's. If you're replacing your current system, then all you'll have to buy is one more XP, and you can just get a XP1600, if you want. As long as you unlock both CPU's, they don't have to be the same speed. You set them both from the BIOS. Of course, you can only do this with the MSI board, since the Gigabyte doesn't have multiplier control.
You can use your current RAM, too. I'm using Samsung PC2700, non-Registered, non-ECC in one of my K7D's and it runs flawlessly @ 150 FSB.
You will take a small performance hit (Video) due to your memory running slower (max of 150 FSB) and some slowdown due to the chipset, but overall, your computing will be faster, because you won't have to wait on any single process to finish, before starting another.
As far as hosting more than one game, I don't know for certain, but I don't think that you can, unless you use dual Network controllers. You might not even be able to do it then. I don't know.
I use my Dual XP system to host games of Ghost Recon and this is, by far, the fastest and best system I have ever used. My single P4 @2.4 GHz couldn't hold a candle to the overall performance of my dual XP1600's @1800 MHz each. Sure, my framerates may have been higher in some benchmarks and stuff, when I was only doing one thing at a time, but this system is fast ALL of the time. I can have a dozen programs running and not feel any slowdown, even when hosting and playing a game. I don't have to wait on CPU-hungry programs to relinquish control of the CPU. The power is always there.
I use dual GC68's on several of my duals, BTW. First is dual XP1600's at 1533 MHz and 1.55 Vcore, using Panaflo L1A fans on the heatsinks (MSI K7D.) The second is dual XP1800's @1.525 Vcore (MSI K7D, same fans as previous.) Third is a Tyan 2460 with dual XP1600's @ stock speed and voltage with stock fans on the heatsinks. Good heatsinks for the money and pretty quiet, although I usually replace the 28 dBA (32 CFM) stock fan with a nice, quiet 21 dBA Panaflo L1A (24 CFM.)