OK guys - read the above and take it to heart. It's an excellent suggestion.
Going through the Asrock (yes, I have one too) is a really cheap way to upgrade that doesn't force you to upgrade gfx at the same time. In my experience it's not the best board out there in terms of raw speed (if you're fussed about small % increases from better memory timings) but the cost and flexibility more than make up for it.
The 6800gt will play todays games more or less fine, and in a month the next gen ati and nvidia cards are comming out - at best this will create even better cards for the same price, at worst it'll push down the current cards like the 7800gt. That said, the 7800gt is a very good card for the money today anyway, it just might be a lot cheaper soon
The OP choice of CPU is great - if you can afford it, the 4400 is a really good chip with a long life ahead of it. CPU isn't all that relevant when it comes to games, and even a X2 3800 is good enough, but if you have the cash the 4400 is a good point on the price/performance scale. Yes, it may not be 'as fast' as a single core, but as long as it is fast enough to not be the limiting factor then you won't notice much real world increase by going single core, instead dual core will provide a better user experience outside of games (or while running something at the same time as a game) as well as a certain measure of future-proofing.