Combo, I didn't have much time to answer before, and wanted to elaborate. The latest version of MS Terminal Services is a pretty fair performer, but it has its limits. Citrix Metaframe is an add-on product to Terminal Services that adds features like session shadowing (what you want), interoperability with other operating systems and non-IP protocols.
The licensing scheme for MS Terminal Services is damn expensive. For each and every seat, you need a NT/2000 server license, a NT/2000 workstation license and a Windows license for the OS on the client PC. That's a lot of cash! Citrix roughly doubles that. The bottom line is that you're spending a whole lot of money for the novelty of running a Windows process on another computer.
No doubt your situation is that the money's already spent and you're committed. Now what? There's no reason to throw good money after bad, so forget Citrix. <a href=http://www.tightvnc.com/>TightVNC</a> will allow you to see what users are doing in a WTS session by allowing you to see what they are doing on their host desktop. It's not as slick as what Citrix has to offer, but in practice it's every bit as effective.
Out of curiosity, what are you using WTS for?
You are false data.