Helen,
I'll enter the lion's den here, as I did once before and the lady concerned seemed to appreciate it, simply BECAUSE I'm not an expert, and feel I can give you useful advice from the perspective of an average user, which is what you are from your description of what you want to do.
Quite simply, today's basic entry level PC will provide you with all the grunt you need for your purposes. I suspect the slowest processor available on a new computer these days is about 2.4Ghz Celeron, which is so far ahead of anything you will need that it is pointless to pay more. Insist on 512Mb RAM, and as MikeD said, the rest of the stuff takes care of itself and you will easily be able to do everything you mentioned. The only exception would possibly be paying a little more for a Centrino processor if you want to get into wireless stuff.
My suggestion as a starting point would be to go to the Dell website, select the bottom of the line desktop, customise it as necessary with your screen/keyboard/mouse, CD/DVD player or burner requirements and check the price. That will give you a good idea of the average price you should be paying, whether you finish up going with Dell or another company. I'd be amazed if you have to pay anywhere near what you mentioned. A bit over half that amount should be closer to the mark at a guess.
Good hunting, and feel free to PM me if you have any questions you think might be best answered by a fellow average user!
