Need upgrade which card would be best compatible with my inspiron 530

Hi,

I have a Dell Inspiron 530. I had a nvidia geforce 8300 gs graphics card with 256 mb but it isn't working anymore. It has completely stopped working and won't install display drivers or appear on my display adapter in the device manager. I think it's completely fried or not working. I need a new upgrade and I'm not too familiar with graphics card. The 8300 gs wasn't working too well with the game current game I was playing, Heroes of Newerth (HoN). I want to know the best Graphics card I should upgrade to and what the power supply is for a 530 inspiron. I've been hearing different things on different forums such as 250 watts 300 watts and 350 watts. The minimum specs for most 512 mb graphics card are about 400 watts and I want to know whether a 9600 GT or 8600 GT would be compatible with the inspiron 530. If not, I'd be happy to hear some recommendations. Which would be the best buy for the inspiron 530 without upgrading the power supply and making it compatible with higher end games and the game I'm playing. Thanks.

My specs:

Dell Inspiron 530 Mini Tower
Operating system: windows vista home premium
Processor: Intel Core 2 CPU 4300 @ 1.80 gHz
2036 MB RAM