Sorry, I didn't make it very clear above.
Do you need monitor, mouse keyboard, windows etc? Or just the box?
For your original budget:
CP-128-IN Intel Core 2 DUO E6600 "LGA775 Conroe" 2.40GHz (1066FSB) - Retail (CP-128-IN)
MB-152-AS Asus P5W DH Deluxe WiFi (Socket 775) PCI-Express DDR2 Motherboard (MB-152-AS)
MY-058-GL GeIL 2GB (2x1GB) PC6400C4 800MHz Ultra Low Latency DDR2 Dual Channel Kit (GX22GB6400UDC) (MY-058-GL)
HD-079-SE Seagate Barracuda 7200.10 250GB ST3250620AS SATA-II 16MB Cache - OEM (HD-079-SE)
GX-022-BG BFG GeForce 7950 GX2 OC 1024MB GDDR3 TV-Out/Dual DVI (PCI-Express) - Retail (GX-022-BG)
CD-041-NE NEC AD5170 18x18 DVD±RW Dual Layer ReWriter (Black) - OEM (CD-041-NE)
SC-032-CL Creative Sound Blaster X-Fi Fatal1ty FPS Edition - Retail (SC-032-CL)
CA-039-AN Antec P180 Advanced Super Midi Tower Case - No PSU (Silver) (CA-039-AN)
CA-013-TG Tagan TG600-U25 600W ATX2.0 Dual Engine Silent SLi Compliant Silent PSU (CA-013-TG)
The 2 hdd are to go in RAID 0. If you don't mind a very slow write time RAID 5 produces the best read with the security of a redundant hard drive. In which case get 5 160gb disks.
The GX2 is there really to represent the G80. You will have to be quick off the ball if you want to ensure one before Christmas though.
Now, if it was me (and keep this in mind that it is my opinion) I would not spend any more than this on the main hardware. With another £1500 to spend I would complain to Dell and get their 30" wide-screen at the US price aka £=~2$ and not "£=$" so around £800 for that otherwise do the same for the 24" one. Add on a good set of speakers, an MX518 and a nice keyboard. Otherwise I will be happy to go crazy and spec up a £3000 'just the box' system.