It's certainly better than your old system - just needs more ram
e4300 £48.24
msi mobo £26.49 (cant find anyone with 1 in stock)
8500gt £26.44
512 ddrs £8.64
maxtor 160 £34.68
sh202 £15.50
£159.99 total for bits ..
ok so a case and psu ontop and not forgetting the operating system ...
thats all i can say really ...
So £30 for a boggo case and PSU + £60 for OEM XP - that brings it to £250 - £50 for the build an install isn't unreasonable.
Last PC I built I charged £400 labour - then again it was watercooled with a custom side panel and paint job
Normally charge £30 for a build - £60 if that's to include installing and patching Windows.