This page is part of a 7-part story, 7 things you can do to make Windows 7 (and other versions) easier to use.
Applies to: All
Why? Sometimes it's a lot easier to find the window you are looking for on the taskbar if it's not cluttered with dozens of windows.
How? It depends on the Windows version you're using.
On Windows XP, download and install TweakUI.
There is no utility similar to TweakUI available from Microsoft for Windows Vista and Windows 7, so you may have to use a third-party utility or make the tweak manually using regedit. See below.
Also, according to Wikipedia, Windows 7 no longer allows fine-grained control of the taskbar grouping via the registry:
The configurable registry option TaskbarGroupSize, which allowed fine-grained control over taskbar grouping  under previous Windows versions is not supported. In Windows 7, users can only configure to either combine buttons, not combine or combine when the taskbar is full.