Help building a new computer

I am searching for a new computer that I could use for gaming, CoDWaW, Protoype, GRID, Some NFS series, Fallout 3, Burnout Paradise, BF2, and others alike. I am definitely looking forward to playing Cod Modern Warfare 2 also. And maybe,just maybe another swing at running GTA4 on a computer....Got it to run on my old PC but it was playable for a little, but mostly it was just lagland.

My old computer (2005) can run those games, but not that great. This is because of the processor, a sad AMD anthlon 64 3200+, a sad 160gb HDD which I am constantly running out of space and the RAM is only 2gb. I do have a Nvidia 9600gt video card, so I don't think ill be needing a dedicated graphics on a new computer since I can install this, as I do have it on my current pc.
I do not need a monitor, a sound system, keyboard and mice. But I could use a new keyboard and a new mouse though. Would like the pc to come with an OS, Vista preferably.

Here are some of my choices of that i could buy, I would prefer not to go over the $750 mark.
1. http://www.bestbuy.com/site/olspag [...] 8096181010
2. http://www.bestbuy.com/site/olspag [...] 8092152723
3. http://www.bestbuy.com/site/olspag [...] 8041999474

I am wondering if choice 1 is any good, because it looks to good to not have any problems with it.
Any links leading to custom built computers on sites like ibuypower.com I could also use.

Thank you for helping.

What's stopping you from building it yourself?

I have the ability to build one on my own, but I'm not really sure about how to put motherboards into computer cases. I also don't know about any local computer shops that are close, except for Best Buy, Staples and stores like that. So I'm not sure where to buy each part.