I'm with Whirly on this seeking to replace rather than upgrade my PC base unit.
John Lewis are doing the HP T340 UK for about £700 and it seems to have most things that a muggins might want now or in the foreseeable future.
Can anyone comment on the ATI Radeon 9200 128Mb video card which it comes with - or anything else for that matter!
Details here
Hope that works,
Cheers,
mcdhu