|my first thought is that "workstation" and "business PC" are just marketing buzzwords: they don't actually correlate to hardware OR software specifications.|
also, i'd verify that your software with the client-server app can be used in the way you're describing: We have some applications with a server back end, but the client portion can't actually run on the same OS instance as the server. Does the server portion run in a Win7 environment, or does it require Server 03/08? Does the client run on a server OS, or does it require WinXP/Vista/7?
so long as you know your software can be configured in the way you're describing, you just need to consider Operating System (Win7? Server 08?) and Hardware (CPU GHz, RAM, etc).
Database applications require a lot of processing power, so you'll want a high-powered CPU, possibly multi-core. Since you'll be running many things at the same time, you'll want a lot of RAM (i'm thinking 4GB MINIMUM). Unless your product development involves some kind of graphics, you won't need to splurge on a high-end graphics card, but some kind of add-in card will help to take processing load off the CPU, instead of "integrated/onboard graphics."
hope this helps!