Gino - would be glad to help.
You use the word "thin client" which can have a specific meaning in the IT world, but I am guessing you mean "inexpensive desktop PC" for connection to the server.
In that vein [desktop PC to talk to a server], a recent 'Dell Deal' that would seem to fit the bill is OptiPlex 380 MT (
http://configure.us.dell.com/dellstore/config.aspx?oc=ftopt38&c=us&l=en&s=bsd&cs=04)
Win7 Pro/3yr basic service/Core2 Duo E7500/2Gigs memory
I would recommend 4Gigs RAM, but the base price of $539 is pretty compelling. Similar pricing from HP & Lenovo.
For a small office, that 3 years warranty and service can be an important feature.