When you plug in a drive on to a WHS Server the only option the WHS Console offers is to add the drive to the storage pool and as you say format the disk. How did you back up the files 1st place and are they a set of separate files or one single backup file.
In order to see the files on the server itself the only option is to work on the desktop of the server itself. A number of bought WHS systems do not allow this as there is no screen port but you can acheive the same effect by running an RDP session
on your PC. Only do the following if you are confident with your systems knowledge as you are bypassing the constraints the WHS Console enforces.
The procedure is to run the program that is in windows called MSTSC which open a dialogue asking for the server name or IP address. Once you have entered that and pressed OK you will get a new logon screen which is the server. Log on and you can use My Computer
to view the disk.
25 years of loving (and too often hating) everything Microsoft.