Dell != AMD, and Athlon64 would appear to be the way to go.
Myself, I'd look at Evesham's Axis range (
http://www.evesham.com ) - I've got a couple of systems from them for home users and they've been pretty good. Around your £2K budget, I'd say:
Axis 64 Dominator (Sep04) 1 £1,105.53 £1,299.00
AMD Athlon 64 3500+ 1 £0.00 £0.00
Microsoft® Windows® XP Home Edition 1 £0.00 £0.00
200GB SATA (8Mb Buffer) 1 £0.00 £0.00
No Raid 1 £0.00 £0.00
1GB ultra fast DDR RAM (PC3200)(2x512MB) 1 £65.00 £76.38
Xpider Design Case 1 £0.00 £0.00
19" Viewsonic VX910 pure digital DVI TFT monitor 1 £0.00 £0.00
16x DVD-ROM 1 £0.00 £0.00
Sony 8x Dual layer DVD re-writer 1 £0.00 £0.00
256Mb NVIDIA Geforce 6800 Ultra Graphics 1 £200.00 £235.00
Audigy 2 ZSsound Platinum drive 1 £120.00 £141.00
Altec Lansing 5100 1 £80.00 £94.00
56K Internal (PCI) 1 £0.00 £0.00
FDD with 7-in-1 Card Reader 1 £20.00 £23.50
Onboard 10/100/1000 Network 1 £0.00 £0.00
Microsoft Cordless Keybd & Mouse 1 £0.00 £0.00
No Mouse 1 £0.00 £0.00
Upgrade to 3 year on-site warranty 1 £34.03 £39.99
No Works V 7.0 1 £0.00 £0.00
MS Office XP Student License 2003 (Retail) 1 £99.00 £116.33
Pinnacle Creativity Bundled Software 1 £0.00 £0.00
No Wanadoo 1 £0.00 £0.00
Totals: £1,723.56 £2,025.18 inc VAT