Sounds like you're looking at a Citrix or thin client solution. This wyse appears to be pretty neat, and they're on special!get 11 for the price of 10. What an offer.

You'd need a Windows server capable of handling a number of terminal clients and you're best to talk to a local business dealer for those. Concievably, any powerful retail PC would do though. getting the Win2k Server & terminal licences wouldn't be chap though.
Why do you need a client thru dialup? Isn't it something you can put on a laptop for demos?