Hello
I'm currently running Xubuntu 8.10 and I've just installed a wireless pci interface to my desktop. So I go to Applications > System > and I notice the Network Manager is missing.. as it turns out it's a listed bug for the Ubuntu 8.10 beta version.
https://bugs.launchpad.net/ubuntu/+source/gnome-system-tools/+bug/248163
-Simple fix all you do is...
sudo apt-get install gnome-network-admin...and the Network Manager shows up again in Applications > System > Network
This may have been triggered by the installation of my wireless interface because I recall opening the Network Manager initially to setup my wired connection when my Xubuntu install was still fresh. Anyway I googled a little bit and didn't find any posts specific to Xubuntu for this bug(I had to look for Ubuntu), so I hope this post saves someone else a few minutes loL..