Yes, any 8800 GT needs a 6-pin PCI-E power connector. If your Power Supply Unit doesn't have one (most likely doesn't since your computer is a little older), then you'll need it. I just noticed the video card I linked you to does come with an adapter for it. You will need to have two available molex power connectors to use it.
Getting more memory will be a waste of time. 2 gigabytes is enough for pretty much any application, unless you are using graphical design applications like AutoCad or you have tons of programs running when Windows loads (which you shouldn't have anyways

). The problem isn't how much memory you have, it is that it is a slower speed.
I would say just try the new video card out and see how Age of Conan runs. You may get good performance if you can adjust the video settings. You may have to sacrifice a bit and lower them, but with the 8800gt, you may find a good balance. If it runs like ****, then you are pretty much in for a major overhaul.
If you can reuse your case and DVD burner, then all you'll need is the new motherboard,
cpu, memory after you have your new video card and hard drive. You won't have much more to go.
It's impossible to tell when you'll need a new video card. The 8800 gt is nearly at the top of the charts right now. There are really only 4 or 5 cards that out-perform it at the moment. It's the best bang per buck card you can get right now, so it is for sure the way to go. If you do have to upgrade in a year and a half, at least you know you got the most for your money on the 8800 gt. If you get say an 8800 ultra, youll spend 300 more bucks and get just slightly better.
The next card to consider is the 9800 GTX. That's the next good bang per buck video card.
