To be honest the second hand market is absolutely SUPERB for anyone looking to pickup a slightly dated, run-of-the-mill machine for general windows work (i.e. not most of the people on this forum!).
I mean the way prices are on older kit, you can get something like a complete ~2ghz/512meg/gf4/60gig/dvd-rw system well cheap, maybe something around the £150 mark?
OK so that's not exactly going to be blisteringly quick, but when you bear in mind that you can barely get a midrange graphics card for that kind of money, that's a pretty good deal for a full PC which would be perfectly adequate for a lot of people.
It's not like the old days, when buying something a few years out of date meant you'd be running low on RAM, constantly paging to a tiny HD barely big enough for windows and a few apps, with no sound/network or burning capabilities.