I did a bit of searching around last month for a relative. After looking in eBuyer, DABS etc, and comparing full systems, bare bones or parts and build from scratch, I then compared with just buying Dell and having done with it.

Which is what I did for him.

Ok, personally, I run and fetch any baubles Steve Jobs throws, so am a mac user, but his Dell is not bad, less than £300.00 (his existing monitor is still good and less than a year old) and I was quite impressed when I set it up. A 500GB hard disk came with it, and if in the same boat as the OP, you can add three more internally, let alone external ones. 1TB internal drives seem to be around the £40.00 mark now if you look for them.

If you don't go for a mega processor then look to see if Linux can do what you want, as it is less processor hungry than Windows. Also, the new Mac Mini is just over £500.00 with a dual core i5 and the best operating system you can get, including iLife with some good software to help you.