I got myself a:
Pentium D: 940
& 2 512meg
How far can I overclock it? and will I need a new cooling fan?
You didn't list your RAM timings and speed. With decent RAM, and good case flow you "might" get 4.0-4.2GHz with stock cooling. With high-end air you might get 4.2-4.3GHz. With water you could maybe hit 4.5-4.6GHz. GL