what do you want to do with it ?
play games = expensive
surf the internet, send emails , do a bit of word processing & spreadsheet work
= get the cheapest you can find as they're all fast enough these days
something in between if you're going to do lots of image editing, or video encoding (which you'll need to do if copying DVDs)
try and get at least a 17" display, 15" are a bit hard on the eyes after a while
ram - 512MB should be OK
hard disk, 80GB should be plenty to start with
do you want a desktop or laptop - laptops are generally more expensive, but easier if you've got space issues or need move it about
anything else can easily be upgraded/added on once you've got the beastie
