If the computer had to be commercially available right now, it would be a Windows Vista Ultimate computer, from Dell. I would get their top-of-the-line XPS 720 H2C computer, with the optional clear-screen side panel. The specs would be:
Intel® Core™2 Extreme QX6850 (8MB,3.67GHz Factory overclocked) (4 super processors, baby!)
4GB Dual Channel DDR2 SDRAM at 800MHz - 4 DIMMs, Corsair Memory.(800MHz. Need I say more?)
2TB Performance RAID 0 (2 x 1TB Hitachi SATA 3Gb/s 7200 RPM HDDs)(2TB, try filling this thing up.)
Single Drive: Blu-ray Disc Drive (BD/DVD/CD burner w/double layer BD write.(A computer with Blue Ray...)
24 inch UltraSharp™ 2407WFP Widescreen Digital Flat Panel.(I'd actually just go out and buy my own TV.)
Dual 768MB Nvidia GeForce 8800 Ultra(Only the best...)
AGEIA® PhysX® physics accelerator(Not sure what this does, but it looks cool!)
Sound Blaster® X-Fi™ XtremeGamer (D) Sound Card(Of course, I'd also get some speakers...)
Logitech G15 Gaming Keyboard (what would be a gaming computer without a gaming keyboard?)
LOGITECH G5 Laser Gaming Mouse (A mouse to match the keyboard...)
19 in 1 Media Card Reader and 3.5 in Floppy Drive (In case it ever comes in handy...)
ATI Theater 650 PRO Combo Analog/Digital TV Tuner with Remote Control(So I can actually watch TV on my TV)
If you don't want to read my post, you could always just go here:
http://configure.us.dell.com/dellstore/config.aspx?c=us&cs=19&l=en&oc=DXCWZH6&s=dhs
lol.