To add a folder to the taskbar, just right-click on the taskbar and choose the Toolbars menu, and then click on New Toolbar.
Just find the folder that you want… in this instance we’ll select the Computer icon and then click on Select Folder.
Now you can see the Computer folder right there on the taskbar. If you click the little arrows it will pop up and let you browse through all your drives.
I always add the Desktop to the toolbar as well.
The same thing works on Windows 7 as well.