The simplest approach is to not struggle with reinstalling Exchange, rather just move the Exchange Information Store(s) from the C drive to the D drive during your next scheduled downtime. I recommend you perform a full backup prior to the move, just in case there is a copy error, and again after the move, because any prior backups cannot be restored once moved.
To move a store, use Exchange System Manager to navigate to the desired IS. Right click Properties and select the Database tab. From there, for the .EDB portion of the file, create a new folder on D. Repeat for the .STM portion of the file. When you click apply, the store will be dismounted, the data moved and the store restarted on completion.
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This was first published in December 2004