[Zeb]

Like nirofo, I've also compiled a parts list but this time from aria (my main supplier) and is Vista ready.

PSU: JeanTech Storm 700W SLi/CrossFire £80 from PC World
One of the components you don't want to skimp on as a decent one really does make a difference. I've got one of these in my machine now and there's a little digital readout on the back telling you what your machine is using power wise. Doesn't always use 700W - mine rests at about 140W when sat doing nothing.

CPU: Intel Coer 2 Duo E6600 2x2.4GHz 1066MHz LGA775
If going dual core go for Intel as they're ahead of AMD. If going for quad core then go for AMD and not Intel - you can see where each company invested their money.

MOBO: Abit Fatal1ty FP-IN9 SLi £140.94
Very nice motherboard overall, enables you to go to 32GB of RAM although Windows XP Pro is stable at a maximum of 4GB.

CASE: Akasa Zen Silent £30.47
Comes without a PSU. I rarely buy cases with their own.

HD: 2x400GB Western Digital Caviar SATAII £135.72
Stripe these for extra data security. If one fails the data is backed up on the other.

RAM: 2xKingston 1GB DDR2 800 (total 2GB RAM) £93.94
Paired RAM for better performance. Kingson and Corsair are the only two brans I personally use.

GFX: nVidia GeForce 8600GT 512MB DDR3 £93.94
You can install another of these at a later date to run side by side for twice the graphics power. Runs in SLi mode.

Total: £654.40 (exl. p&p)

Chances are you might even be able to save some money by using certain parts from your existing machine like DVD drives, mouse, keyboard, card reader etc.

If your current machine came with XP pre-installed or you only have XP Home then I'd add about an extra £120 on top as you'll need Pro to handle the dual core CPU. I'd stay away from Vista for a while as not all drivers for all hardware are available yet and I know a few people who've gone back to XP because of it.

Attached is a screengrab of my task manager showing two processors in XP.