LXDE does have it's own Network Manger called LXNM. It works with the netstat LX Panel plugin (To enable: Right-click Panel, Add Panel Item -> Mange Networks).
However, I haven't tried it except in a VM, and it appears a little too basic for wifi. Although a VM doesn't have wifi, so perhaps someone can set me straight?
In any case, it does bring up right-click options to Repair or Disable a connection. While Repair just restarts the network connection, Disable appears not only to disconnect, but also removes the panel plugin icon too, so it is impossible to re-enable again through the GUI. Not exactly user friendly to deny an undo feature for something so basic!
If you have done this, the following should restart the connection (and cause the plugin to reappear on the panel):
sudo ifdown eth0 sudo ifup eth0
Obviously, you would need to substitute eth0 with your network interface name (although all wired LAN connections tend to be eth0 as default).
Anyway, if LXNM isn't good enough for you, consider Wicd.
In order to install, simply follow the advice on their website. Obviously, some things will need to be done command-line style, due to the lack of Synaptic etc. You can install using apt-get (recommended - as detailed below), which will maintain the most recent Wicd for you each time apt-get upgrade is run, or simply download the .deb file from the appropriate Wicd repository as a once off install.
gksudo leafpad /etc/apt/sources.lst
Then add the following line to the bottom:
deb http://apt.wicd.net hardy extras
wget -q http://apt.wicd.net/wicd.gpg -O- | sudo apt-key add - sudo apt-get update sudo apt-get install wicd
That's it. It's now installed.
In order to get the icon to appear correctly, the .desktop (in /usr/share/applications) needs to be edited (see Menu). The icon is located in /usr/share/pixmaps/wicd/wicd-client.png, so just change the appropriate line to Icon=/usr/share/pixmaps/wicd/wicd-client.png and do the same for the Icon[en_US] reference.
Wicd installs to default autostart the System Tray applet. That obviously means the process is running all the time, using your valuable system resources. In order to disable this, just delete the wicd-tray.desktop file labelled as Wicd Network Manager Tray (or rename to wicd-tray.desktopbkp), as described in Autostarted Apps..