It looks like you have a good idea but I would make three main decision changes.
1. The processor is an old Intel Pentium D, by the looks of it and is based on Intels old NetBurst Technology. I would recommend upgrading that to a faster, almost equivalently priced Intel Core 2 Duo. They are by far the better processor and it will last you longer.
2. The Case you have chosen may not be big enough for the new nVidia 8 series cards, it probably is but perhaps do a little research. I am 60% sure it will be fine though, as it is usually the bigger nVidia 8800 series cards and the new nVidia 9800 series that tend to be larger.
3. Definitely go for a much better power supply, 500W is fine but I wouldn't trust a make I have never heard of and on the grounds its SO cheap. You do not want it to blow or go wrong as it will be you hardware that will suffer. I would recommend going for some slightly better ones like CoolerMaster, Antec, Hiper and ThermalTake etc.
I hope this helps you, I would say the power supply is the most important thing you would need to upgrade though as explained in point 3. Points 1 & 3 are most important.
Cheers. :D