You won't find many 256bit cards for that price. If you do they will be "le" or "pro" versions and probably slower than the 128bit counterparts anyway.
Ok before I discuss the video card I want to say that your ram choice is poor Don't get 512MB or really good ram. Get 1 GB or whatever you can afford. 512MB won't be enough, 1gig is preferred.
So with that in mind get the 6600 gt probably or however you want to budget that.
Since you picked the 4400 ram that indicates you want to overclock. There should be some cheaper ram that will overclock reasonably and you can afford a gig of it.
The x800 xl is probably out of budget but it would be a nice upgrade.
Would also recommend a better motherboard if possible but I know you're on a budget so just work in what you can.
And does that board even support dual channel ram? If not that sucks, and you would need a gig for sure.