I'd say the X2 3800 based system is better value for money although the other may be a little faster in gaming. I would however recommend building it yourself as you save a fair bit, I don't think I have missed anything important out but even including delivery you save around £200, the graphics card is an XT rather than an XTX but you can overclock or fit it into the budget, the Ram is as good, XP Home rather than Pro but unless you need the additional networking features of Pro I'd pick Home anyway to save some cash.
OS-001-MS Microsoft Windows XP Home Edition inc. SP2 - OEM - 1Pk (N09-01528) (OS-001-MS)
£51.95 £51.95
CP-152-AM AMD Athlon 64 X2 Dual Core 3800+ (Socket 939) - OEM (CP-152-AM)
£139.95 £139.95
MB-129-AS Asus A8R-MVP Crossfire (Socket 939) PCI-Express Motherboard (MB-129-AS)
£61.95 £61.95
MY-007-GS G.Skill 2GB DDR ZX PC3200 (2x1GB) CAS2 Dual Channel Kit (F1-3200PHU2-2GBZX) (MY-007-GS)
£119.95 £119.95
GX-047-CO Connect3D ATI Radeon X1900 XT 512MB GDDR3 AVIVO TV-Out/Dual DVI (PCI-Express) - Retail (3056) (GX-047-CO)
£219.95 £219.95
HD-018-SA Samsung SpinPoint P SP2504C 250GB SATA-II 8MB Cache - OEM (HD-018-SA)
£43.50 £43.50
CD-035-NE NEC ND3550 16x16 DVD±RW Dual Layer ReWriter (Black) - OEM (CD-035-NE)
£19.95 £19.95
FG-000-AR Arctic Cooling Freezer 64 Pro CPU Cooler (Socket 754/939/940) (FG-000-AR)
£14.50 £14.50
BU-000-AK Akasa Eclipse 62 Aluminium Case & Window (BU-000-AK)
CA-006-AK Akasa Eclipse 62 Window Side Panel (CA-006-AK) 1
CA-005-AK Akasa Eclipse 62 Aluminum Case (CA-005-AK) 1
£82.70 £82.70
CA-008-TG Tagan TG530-U15 530W ATX2.01 Easycon SLi Compliant Modular Silent PSU (CA-008-TG)
£61.95 £61.95
Subtotal £816.35
VAT £142.87
Total £959.22