Gail, new piece of information here: turns out the SQL Server binaries are not installed on this drive, but some of the typical folders are there:

D:\SQL\MSSQL10.MSSQLSERVER\MSSQL

>> DATA

>> FTData

>> Jobs

>> Log

>> repldata

The Data folder has the master, model, and msdb system databases

The Log folder has the default trace, errorlog, and sqlagent log files

So my plan now is to plan a complete maintenance window to take the MSSQL Service down, copy the entire folder structure from the external array to the internal, rename the drive letter, restart the service.

This should work right? I mean, SQL shouldnt' know the difference as long as everything is still pointing to the proper drive letter it was installed on?