If you use Windows’ built-in feature that groups similar program windows on the taskbar, you’ve noticed it only works when you’ve launched enough windows to fill the taskbar. The CyberNet blog offers up a customisable registry tweak that activates the grouping with just two or more windows open. Not everyone enjoys the grouping function, as it was downgraded to a non-default setting in Vista, but for those who do, the hack can be a real helper. You can download a registry fix file at the link below, or make the change yourself at the following key:
HKEY_CURRRENT_USER \ Software \ Microsoft \ Windows \ CurrentVersion \ Explorer \ Advanced
Create a new DWORD (32-bit) value named TaskbarGroupSize at that location, setting the value to 2 or higher to set the number of programs to activate the grouping.