[thephilosophizer]

Looking at your system specs, I am wondering what level card you will need. The 9600gt is essentially the same card as the 8800gt, just stepped down a bit, but I doubt it is a difference you will notice. I don't know this part for sure, but I think it may have slightly less power consumption as well. I have heard people running after market cards on the stock psu's, it might not work, but it may be worth a try.
Installing a different psu won't be particularly hard, though it will be somewhat time consuming, ie, not a five minute fix like a gfx card or ram, etc.