Windows 7 tips and tricks : Windows Vista taskbar

Right-click on the taskbar and choose the properties dialog. Select the "small icons" checkbox and under the "taskbar buttons" setting, choose "combine when taskbar is full".Starting explorer from "My Computer"

To do this, navigate to Windows Explorer in the Start Menu (it's in the Accessories folder). Then edit the properties and change the target to read:
%SystemRoot%\explorer.exe ::{20D04FE0-3AEA-1069-A2D8-08002B30309D}