Well after a bit of crafty bidding on ebay, i have managed to get another 4Gb Corsair Xms DDR2 for £28 and a second Asus HD5770 the same model as my existing one for £56, total cost of upgrade £84.

which makes my old rig now look like this:
Core2Duo E6700 2.66Ghz Cpu
Zalman Cpns 9900 Cpu Cooler
8Gb Corsair xms DDR2 800mhz Ram
Asus P5W DH Delux Mobo
Corsair 700w Psu
Two Asus HD5770 Gpu's in crossfire
Corsair 60Gb SSD Hdd (boot)
two Seagate 500Gb Hdds (storage)
Razer AC-1 sound card
Windows 7 64bit
All running at 1920 x 1080 res
Should that be enough to power BF3 smoothly till i can afford a new rig ?
The Fail Cakes are on me !................