Nicole,

Even though the drive is not listed, you can use a UNC path to backup to. Even if you receive a path error, you can use the default share for the drive or create a folder and share it on the drive that you are attempting to backup to.

If no share: \\SystemName\DriveLetter$ (example: \\Server1\F$ )

If share created: \\SystemName\Share

Just beware though, that the Log On As account used to run the SQL instance must have access to the path in order for the backups to be successful.

Hope this helps!