Vista may use a bit more resources than XP, but with sufficient ram; you probably wouldn't notice, when it comes to gaming or pretty much anything else for that matter. Personally, I would get Vista; since it comes with a coupon for Windows 7 anyway. I think that is better than being stuck in the age of XP for years, and years. Unless you are really set on XP, than go ahead. It's not my money to spend.
You generally don't need a 1GB card. I don't know why you keep saying you do. Unless you have a high resolution monitor, you won't really see a difference, but you know; Again, I'm not going to tell you what to spend your money on. It's your money after all. GTA4 does take a lot of RAM though. -_- Very poorly managed.
It's up to you if you want to build or buy it prebuilt. It doesn't really matter to us, so if you want to build than build. If not, than buy a prebuilt. If you don't want DOA parts, than buy a prebuilt. But seriously, don't come in here saying stuff like trying to be a smartass or something, like you trying to tell us something that you think that we don't know, when we do know. Buy a prebuilt then, noone in the long run here cares how you spend your money. We are trying to help you make a decision, but you don't seem to want to agree with anything we say.
Buy a 4850 or something better if you want to game, the card you listed is pretty bad with more recent game. 4850 is a great budget gaming card. You could look at the 4770 if you want something with a little less power consumption for around the same performance.
Also, ~10 bucks for a quicker shipment isn't all that bad. Especially when you are spending ~600 dollars for a computer. If you don't want it don't get it. Prebuilt is the same deal, you will probably spend more than 10 dollars than you would building the thing.
