Dell knocked a real big chunk off the price of this sometime today.
Available with Vista or XP if you follow my links with the same spec otherwise.
Remeber to reduce the warranty to minimum and buy via Quidco for further cashback savings.
305-D03921a - £563 or less delivered
Intel® Core 2 Duo E6300 Processor (1.86GHz, 1066MHz, 2MB)
Genuine Windows Vista Home Basic - English
Dell 20" Black Wide Flat Panel (E207WFP) - UK/Irish
1024MB Dual Channel DDR2 667MHz [2x512] Memory
320GB Serial ATA RAID 0 Stripe [2x160GB 7200rpm drives with DataBurst cache]
16X DVD+/-RW Drive
256MB ATI® Radeon® X1300 Pro PCI Express graphics card
Integrated Audio with Dolby Digital 7.1 capability
Dell 2 Button USB Scroll Optical Mouse - Black
Internal 13-in-1 Media Card Reader
McAfee® Security Centre 8.0 - 36 Month Protection - English
Microsoft® Works 8.0 - English