if you always had this problem then getting a new card may help reduce the temperature. but i don't think that's the reason you are having heat issues. on average, with heatsink that's properly bleeding off heat the way its supposed to, the idle temps on a pentium D should be around 40C and full load should be around 55-60C (with stock cooling)
70 is high but still within limits
seems to me that inefficient heat transfer is the problem.
my suggestion is that you should go get a thermal paste called Arctic Silver. Clean and reapply the paste and reseat the heat sink (use the smallest amount u can to cover the processor)
then test to see if your temperatures come down
if they dont,
download a program called Prime95, its a stress testing tool that tries to calculate the largest prime number. it places your processor under the max possible load and verifies stability.
run it over night and see if the system is stable at 70C. if it is then don't worry about the temps and just use the system as normal
if you get errors in the calculations (it will tell you) then your system is too hot and something needs to be done. You can invest in a better heatsink to bleed heat or get a new video card.
under normal circumstances, i wouldn't disagree with Phinds but i would recommend a new heatsink. its better for dealing with heat and in almost all cases cheaper.
but really, if you have a Pentium D processor, you should really be looking at a new computer not a new heatsink or graphics card, especially since you are gaming.