The new Core 2 duo cpu's are in all the Systems in this thread.
I will start with the cheapest available.
307-D09925a - £679 delivered or less!!!!!!!!
Intel® Core® 2 Duo® E6300 Processor (1.86GHz, 1066MHz, 2MB)
Genuine Windows® XP Home Edition (Does not include Operating System Re-installation CD)
1024MB Dual Channel DDR2 533MHz [2x512] Memory
250GB (7200rpm) Serial ATA Hard Drive with 8MB DataBurst cache
16X DVD+/-RW Drive
256MB ATI Radeon® X1300 Pro PCI Express graphics card
Dell 19" Value Flat Panel (E196FP)
Integrated Sound Blaster Audigy ADVANCED HD Audio Software
Dell 2 Button USB Scroll Optical Mouse - Black
Internal 13-in-1 Media Card Reader
Microsoft® Works 8 - English
Remember to reduce the warranty to minimum and buy via Quidco for cashback savings too!