If it's for gamming, and your not bothered about future proofing, just for games right now, go the Athlon. If your looking at 2 years down the line, go the Intel. AMD might compare far superior right now, but when Multi-threaded and longer 64bit coded games come out, the pentium D might be a better option.
What Pentium D is it? 8xx, 9xx something else?
In all seriousness though, your better waiting on the Conroe if your current setup can do you the now.