By default there is a hal policy that might block you from seeing any additional drives, and or partition's you might have connected.
look in /usr/share/hal/fdi/policy/10osvendor
you should see a policy named 99-storage-policy-fixed-drives.fdi
. This policy by default prevents you from seeing any additional partitions. You can safely remove it... and or rename the file. I had ran into this problem with new install of Gentoo a ways back. I had to edit the policy to accustom my needs.
You go to this site here
and get more info on hal's policies.
jman82s - post was the most accurate to your OP. This does in fact show the mounted icon, when the partition is mounted. Though if your missing the disk or partition all together then you need to first follow my instructions then jman82s.