Dell xps 720 for my son

I need help. I want to buy a computer for my son that he will be able to play his games on. He just got Oblivion and on his year 2 yr old AMD 3500 Medion with a Nvidia 7600 video card he can't play it very well (with two meg of ram) I am going through chemo right now and he is taking care of me and I want to do something for him. I can't afford to buy one of those extreeme game machines, and I can't and he can't build one on his own. So I am on the Dell web site and this is what I have put together. One thinig that I am questioning is is the ram. Even though it is a better ram and overclocked, it does not give me an option to go to 4 megs of this ram, which I am not sure is necessary or not. I can't find it (that ram) for sale either anywhere on the web to the same specifications to see if I could add more later if nec. Here is what I picked out for him. Please offer me whatever comments you can. The price comes to $2,634 as configured.

PROCESSOR Intel® Core™2 Q6600 Quad-Core (8MB L2 cache,2.4GHz,1066FSB) edit
OPERATING SYSTEM Genuine Windows® XP Media Center 2005 Edition with re-installation CD edit
MEMORY 2GB Corsair Dominator DDR2 SDRAM 800MHz OC'd to 1066MHz-2 DIMMs edit
HARD DRIVE 320GB - Seagate 7200RPM, SATA 3.0Gb/s, 16MB Cache edit
OPTICAL DRIVE Dual Drives: 16x DVD-ROM Drive + 16x DVD+/-RW w/ dbl layer write capable edit
MONITOR 20 inch UltraSharp™ 2007WFP Widescreen Digital Flat Panel edit
VIDEO CARD 768MB Nvidia GeForce 8800 GTX edit
SOUND CARD Sound Blaster® X-Fi™ XtremeMusic (D) Sound Card edit
KEYBOARD Dell USB Enhanced Multimedia Keyboard edit
MOUSE Dell Optical USB Mouse edit
FLOPPY & MEDIA READER No Floppy Drive or Media Reader Included edit
MODEM 56K PCI Data Fax Modem

Ideally -- you could go to a local computer store and get them to build you one for ~$50. Either way, some suggestions:

-I would try to find a monitor and ram somewhere else. I mean...100$ for a 1 gig module? 200$ for a 20' lcd? Seems a little expensive to me.

- Even though it's not exactly the greatest option right now, why not go for vista? You Probably wouldn't want to install another os later after service pack 1.