Back up to secondary HDD over network?

[Paul_G]

Originally Posted by dnanian

You should be able to see the volume using regular "File Sharing", Paul...

Well, that's what I thought too. Which makes me think I'm doing something wrong, because I can't seem to.
Here's what I'm doing: I click on Network, and then choose the G5. That shows a graphic saying "To see the available shares for the server G5, click Connect".
I do so. A popup appears: "Connect to the fileserver G5. Connect as Guest/Registered User."
I enter the name and password: it says "G5. Select the volumes to mount", with a list of the various users. I choose "Paul", and it mounts Paul as a disc on my sidebar.
So, now I can access all files that are on the User "Paul". But I can't see how I can use that to access the secondary HDD, which is where the space is for the backup. I could mount other users instead, but they are all on the G5's main drive too.
Where am I going wrong? How do I navigate to the second HDD? I'm sure I'll feel silly when I hear the answer...
Thanks in advance folks.