6600 GT <------- there is a E-PCI and AGP version...is this important enough to base my system around an EPCI ?
It's PCI-E not EPCI
Your mobo has to have a PCI-E slot which your current one doesn't.
Basically all you really need to do for that setup dude is get that 6600GT....if you get it from eVGA within 90 days if you have more money you can upgrade to the 6800GT by paying the difference between what you paid for the 6600GT and the cost of a 6800GT ($399.99) so basically if you pay $199.99 for a 6600GT, within 90 days if you have $200 more you can upgrade to the 6800GT, it's a pretty good deal.
Don't bother upgrading your RAM, valueRAM will be fine for your uses and I can guarantee you you won't notice a substantial increase in speed going from valueRAM to high performance RAM. High performance is only worth the price if you overclock em