TSQL - CMDShell - Batch File - Map Network Drive - Access Denied

*big sigh*
I'm trying to replicate a previously working process. These were the basic steps:

- SQL 2000 MSDE dumps multiple databases to a backup folder on the same server via a scheduled SQL job. *Works Perfectly*
- The last step in this job was xcopy D:\MSSQLBackups\*.bak \\backupserver\share /v /d /y
     *Yes it was a step type of 'Operating system (CMDExec)'
-The xcopy never occurs and the job history shows:
   " Executed as user: SERVERNAME\SYSTEM. Invalid drive specification  0 File(s) copied.  Process Exit Code 4.  The step failed."

-The owner of the job is a domain account which has proper privileges to the source and destination shares/servers.

I tried to 'step' through the process by using the xp_CMDShell command in a TSQL query window.

Query:
EXEC master..xp_CMDShell 'xcopy D:\mssqlbackups\*.bak \\BACKUPSERVER\SHARE /v /d /y'

Result:
Invalid drive specification
0 File(s) copied

I proceeded further and created a batch file with some DOS commands to see where the command was running from and to obtain other information

Query
EXEC master..xp_CMDShell 'D:\MSSQLBackups\CopyDB.bat'

Batch file contents:
cd\
D:
net use Z: \\BACKUPSERVER\SHARE
Z:
xcopy D:\mssqlbackups\*.bak Z: /v /d /y
net use Z: /delete

Results:
C:\Windows\System32>cd\
C:\>D:
D:\>net use Z: \\cork\sqlback$
The command completed successfully.
D:\>Z:
Access is denied.
D:\>xcopy D:\mssqlbackups\*.bak Z: /v /d /y
Invalid drive specification
0 File(s) copied
D:\>net use Z: /delete  
Z: was deleted successfully.
(20 row(s) affected)

How can I find out what account is being used to access this mapped drive?

-Stumped