Howtogeek posted a guide about pinning an external drive to the Windows 7 taskbar

Do you have an external drive connected to your Windows 7 computer and would like to access it from the Taskbar? Here we show you a work around that will allow you to pin it to Taskbar.

Adding Drive to Windows Explorer
You would think the process would be as easy as dragging the external drive icon to the Taskbar. Unfortunately that isn?t the case. If you try to drag the external drive icon to the Taskbar, it just adds it to Windows Explorer.

Then if you right-click on the Windows Explorer icon, you?ll be able to access it from there. This might be enough for some users, but we want to add it to the Taskbar as an icon.

  How To Pin an External Drive to the Windows 7 Taskbar