I found this in a few different places around the 'net - hopefully it's helpful:

Create a Keyboard Shortcut to Open a Folder

Do you have a folder to which you want instant access from anywhere on your computer? For example, if you want the My Music folder to pop up while Internet Explorer or Word is maximized, follow these steps:

• Select the folder in Windows Explorer.
• Create a shortcut, and place it on the desktop. (You create a shortcut by opening the folder, pointing to New on the File menu, then clicking Shortcut. Drag the shortcut to your desktop.)
  
• Right-click the new shortcut, and then click Properties.
• In the Properties dialog box, click the Shortcut tab, and in the Shortcut key box, enter a Control key combination or a Control-Shift key combination, (that is, Ctrl+Alt+M or Ctrl+SHIFT+M when M is for music), and then click OK.

Anytime you hit the key combination you specified, your folder will open, even when other programs are maximized! This tip can be applied to folders, programs, and text file shortcuts that are placed on the desktop.