My first question would be why? You do mean the
workspace? right. You are also allowed to add content
sources of differrent types which you can point to
that drive. My experience is that IIS is the anchor to
SPS. Moving the work space sounds like you are asking
for trouble.

Actually,

I just want to move the storage  of the WSS.MDB from my C drive  on
the server  to the D drive where there is far more room for it.

Not moving  workspaces, just the storage file.

Try SPSUTIL utility avilable in Resource Kit. It allows your to move
the store and log files  to a differant machine. This also increases
the performance of SPS.

Hope that helps you let me know of any problems as i have done this
before.

If you go into the properties of your SharePoint Portal Server, there
will be a tab called "Data". This tab will show you all the current
locations of all the system files  and logs including the WSS database.
You can click on the browse button to navigate to the new location. If
you read the description, the last sentence states:

"If this location is changed, the file is moved immediately"

I've never tried to do this before but if anybody has, feel free to
provide any inputs on my recommendation.