If you are interesting in more gaming than apps, or even maybe 50/50 between the two, then go with an AMD 64. I would SUGGEST going with the socket 939 boards, as everyone here says they are the future (I don't know for sure).
About which AMD 64bit...?
Well I would suggest you look at your budget, you will notice that the 2939's make a price jump right after the 3500+, which is a great chip and many people here have it so they will tell you how it is im sure, if you ask them.
But, if that is a little high for your budget, then I would suggest a 3200+ in the socket939. Or the 3400+, which is a level up, but MAKE SURE you are looking at the s939 version, not the 754.
Im not exactly sure the exact equivilant of a 4.0ghz intel = AMD...
But I would bet some money that the AMD 3500+ would outperform it in any game.