"HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\W
New > DWORD (32-bit) Value
"TaskbarGroupSize"
Double-click new entry and set value to "0"
This is the secret to making all the task-bar windows in Vista (and I believe XP) group together whenever there's more than one. I am so much happier now that all windows of the same program group into one task-bar button before the entire task bar is cluttered.