The question is if the money isn´t wasted on the new processor put into the old socket 939.
If you want to stick to your mainboard I´d suggest getting a single core as 3700+ or 3800+ for little money. I´ve overclocked my 3700+ San Diego from 2.2 to 2.8 Ghz and it´s running LFS fine at 1680x1050, 8x AA, 16x AF using a 8800 GT which I would prefer instead of a 9600 GT, if you want to use AA.
In additon to that other games run fine at full quality and 1680x1050, 4x AA, 16x AF like CoD4, Rainbox Six Vegas, GTR2, Kane and Lynch...
The x2 4200+ runs at 2.2 Ghz and will give you almost the same performance as your current cpu.