Fran
For those specs, and they are top of the line, you will need at LEAST a 500watt power supply. If you can afford it, a 750 watt one is preferred so you will have enough extra power to run those heat generating specs. If you are buying a built machine, don't let them send you home with a minimal watt power supply or cooling fans.
The 8800 GTX is the best graphics board you can find but at a steep price tag. It is DirectX 10 ready so you will be able to run the next graphics format without any need to upgrade later. It is superior to the ATI card which isn't Direct X 10 capable yet to my knowledge.
Good job in your choice of components.
I'm in the market for an upgrade and those components are identical to the ones I will be choosing.