If by budget gaming rig you mean $600 or less, then AMD is OK.
AMD has no advantage over Intel if you are planning to spend at least $100 on a CPU.
Let me spell it out:
AMD Phenom 9850 - $170 and any overclock you manage will improve performance perhaps 5%.
Intel Q6600 - $180 and will easily overclock far beyond stock. Probably a 25-33% gain in performance.
Even on your system, most games will run 5-10 FPS slower on the AMD at stock speeds.
The new AMD Phenom II 940: Slightly faster than the Q6600 for around 90 dollars more. Will probably overclock at least as well as the Q6600. Cannot compete with an actual fast Intel CPU such as the i7 920, which costs about the same as the Phenom II.