A drive may help an SSD woudl help for sure but is a bit pricey. When it comes to increasing performance on games the Video card $ for $ is the best upgrade you can make but be aware in doing so you may need to upgrade the PSU as well.

The question is what games are you tryign to play and what video card are you currently using?

I had a friend who was playing the Sims2 on her PC and she told me that when she told the Sims to go downtown that she literally had enough time to take a shower and return before the downtown area would load.

It turned out that she had the onboard SIS video. I had a GE Force 7100 card laying here that I threw in and she was thrilled with it, Load times were 1/10th what they were before and the whole game played much better.