This little tweak allows you to customize the grouping action on your taskbar. According to the default, if you have more than (ex.) 3 internet explorer windows open, XP will group them into a single button with a menu that lifts off the taskbar. You can change the number of windows that are open before XP groups them.
look for the dword "TaskbarGroupSize"
If it isn't already there, right click on the right pain, and create a new dword value. Double click the value, and enter the number of windows you want xp to allow open before it groups them. I personally like 2, because I like any related window to be grouped automatically, but, you can set this high if you wish.