The Opteron 144 should perform adequately as a gaming CPU. If you are thinking about future upgrades, I think that the purchase of a motherboard like MSI's K8T Master2 FAR might be a good choice. You could drop in the 144, and later upgrade to the fx-51 or fx-53. Additionally, if you decided to drop in a 200 series (244 = $130 more than the 144), you could purchase a second processor later, and have a very powerful 64-bit dual processor machine. Drawbacks? Of course, not many applications take advantage of both processors, and all this will cost you $$$.
In the mean time, the 144 should run your games at least as well as an Athlon 2800 - 3000. Good Luck!
Underdog