250GB seems like quite a small hard drive for your usage. As a guide, look at the total *used* space on your current drive, double it then double it again. That will give the size drive you should be looking at.
Do you already have the operating system, or is that to be included in your budget?
As a personal thing, i'd steer clear of the Phenoms. The Intel range is far better, IMO.
the Pro version, including OS comes, to £739.