ok i think everyone has gotten all excited about the PC and forgot about ken!
Ken, what do you want to use on the computer and what do you want to be able to do?
do you want to use photographic programs such as photoshop to edit photos, or are you just going to be viewing stuff?
are all you going to be doing is using the web, and looking at stuff on the web?
are you going to be playing games?
If you after a 'web machine' only, and all your going to be doing is looking at stuff on the internet, then the 256MB will be fine with windows 98. XP does like 512MB RAM but it can survive on 256MB RAM.
now the modem.... is the modem on your old machine an external modem (ie is it a small box outside of the computer you put your phone line into), or do you plug your phone line into the back of the computer? If it is an internal modem (plug into the back of the computer) then you will have to ask if the guys in the shop can add that from your old machine into your new one.
are you confused yet?