An idea on budget would help narrow things down a bit as well, but consider that for around the £500 mark, you should be able to get a reasonable PC, with a 19in Flat screen, and ideally 2Gb of RAM, with a 200Gb Hard disk. THe processors are all faiirly up to the job these days, unless you are wanting to run things as a gaming machine. Also consider what warrenty you get, as in when it goes wrong, what happens, will they come and pick it up, or do you have to stuff it in a box, and send it back to them.
Just my thoughts,
all the best
AAF