Stan,
I bought a Dell P3 500 a few months back for £1600 (Irish). Now I bought a load of extra stuff with it (CD re-wrtier, scanner, etc), but you'll get a basic system off them for considerably less in the UK (not sure exactly how much).
http://www.dell.com is the place to go.
I have used a lot of different makes over the years and I wouldn't touch anything else...FS2000 runs like a dream, but you can't make copies of the Cd - not that I'm suggesting anyone would do that!!
They also do Intel celeron processors as well, which are a bit cheaper. As WX points out the AMD chips ahve a very good reputation now and are condsiderably cheaper...
The sim itself is a big improvement over 98, both in terms of graphics and flight dynamics, and already there are tons of downlaods available...