This probably applies to either Vista or Windows 7...they both have a feature where it will group windows from the same app under a single button. However I have one application I want it to never group -- specifically an X11 server, where different windows are separate apps and not related (ie, I don't want it grouping my xterm window along with my accounting software window, just because they are both owned by xserver.exe).
I don't want to turn it completely off, I like when it groups all my Explorer windows together for example. I just want to exclude/whitelist/? a single application, xserver.exe, from having its windows grouped.