Share one computer to multi-users simultaneously...Pro & Con?

Dear all:
(this is also posted at Other Hardwares, but I figure many system engineers browse this forum as well...)

I am trying to find a solution to make our warehouse process more efficiently. I figure that I need extra shipping servers (one more for UPS and one for FedEx). One way is to simply purchase two additional desktops and hook them up. Alternative choice would be get a software to host one computer for multi-users at same time.

I would like to know, if any of you ever have done this, is it worth doing? Any pro and con? Any recommanded software? I searched and found www.thinsoftinc.com has some cool stuff (although they charge you $99 per user license).

Thanks a bunch =)