I'm sorry that I didn't read your other threads, as I knew there were a LOT of people having problems with the 6600GT AGP cards, irrespective of what make they are.
If you have a look on the Nvidia forum ( click here )there are a lot of threads on there that are about people having problems with this card.
This thread is useful if you're having problems with it click here
Your advice, Ballie, is good. If you can't get your 6600GT AGP card to render using DirectX, you most probably have a duff card and it should be returned to your supplier(or you haven't connected your card up to the PSU :) ).