Right click the explorer icon and click on Properties. The box labeled Target determines where Explorer opens. For example, adding   /n, /e, /select, C:\   to the end of the target will have explorer open with all the drives showing instead of Documents. I haveb't tried to get it to open in a specific drive, but google on the topic and you will probably find it. Found it! Just use /n, /e, C:\ to open in C: Here's the whole address. Be sure to add the spaces and commas: %SystemRoot%\explorer.exe /n, /e, C:\
In Xp it is possible to customize where explorer opens...ie C: or D: drives.  The properties are altered in explorer to enable this. What is the script to enable Vista such a feature?
Windows Explorer Question on Vista