Something like this might be suitable, I picked the Hanns-G because it has a DVI port. You can't quite fit 2gb into the budget without skimping on other parts, if you went with an 80gb hard drive you would still probably be about £20-30 overbudget which might well be worth it anyway.
MO-017-OK OcUK Value Hanns-G HW191D 19" Widescreen LCD Monitor - Silver (MO-017-OK)
£121.99 £121.99
CA-067-AN Antec NSK6500 Super Midi Tower Case - 430W PSU (CA
£58.99 £58.99
MB-004-AK Asrock Conroe945G-DVI (Socket 775) PCI-Express DDR2 Motherboard (MB-004-AK)
£45.99 £45.99
CP-135-IN Intel Core 2 DUO E6300 "LGA775 Allendale" 1.86GHz (1066FSB) - OEM (CP-135-IN)
£99.99 £99.99
HS-017-AR Arctic Cooling Freezer 7 Pro CPU Cooler (Socket 775) (HS-017-AR)
£14.99 £14.99
CD-042-NE NEC AD5170 18x18 DVD±RW Dual Layer ReWriter (Silver) - OEM (CD-042-NE)
£18.99 £18.99
GX-042-OK OcUK GeForce 7900 GS 256MB GDDR3 TV-Out/Dual DVI (PCI-Express) - Retail (GX-042-OK)
£97.99 £97.99
MY-083-CS Corsair 1GB DDR2 Value Select PC5300 Dual Channel Kit (2x512MB) (VS1GBKIT667D2) (MY-083-CS)
£72.99 £72.99
HD-079-SE Seagate Barracuda 7200.10 250GB ST3250620AS SATA-II 16MB Cache - OEM (HD-079-SE)
£51.99 £51.99
Subtotal £583.91
VAT £102.19
Total £686.10