There's another firm that sells a mix of second hand, failed orders etc. from Dell. I think it's ITCsales.co.uk and I have used them a few times.
A pal got a bargain Compaq from PC World £189 for Pentium something or other 160 gig disc, 1 gig ram, no screen or keyboard and XP Home but what a price.
I couldn't build a PC for the money Dell sell them but then they stuff you on delivery.
Mike