Typically, Explorer launches with My Documents (XP) or the Documents (Vista) folder opened.

However, this can be changed to open a folder of your choosing. First, create a shortcut to Explorer on the Windows Desktop or Quick Launch bar, right-click on it and select Properties. Now click the Shortcut tab and, in the Target section, click just to the right of the ‘explorer.exe’, hit the spacebar and then type (for example): ‘/e,d:\’, without the quotes. This example would have Explorer open the D: drive.

If you want Explorer to launch and display a different drive, just change the d:\ part to the appropriate drive letter. Similarly, if you wanted to open a specific folder, the format would be: /e,d:\FOLDERNAME.
Ian Plowman