I'm a bit late replying here. Maybe you have already solved it.
Just to be clear, though, you don't need to use the XFCE desktop to use the power manager. You say you are using R8 LXDE 32 bit. That's what I have and the XFCE power manager was installed at the initial installation and is working with my LXDE desktop. If I right-click on the battery monitor icon and select "Preferences" it brings up the dialogue that madjo refers to.
So, you can check if the power manager is installed in Synaptic Package Manager. It is called xfce4-power-manager. If it isn't installed (did you remove it?) then just do as madjo says.
Does your bottom panel have the system tray included in it? You can check this by right-clicking in the panel, then "Panel Settings" and then the "Panel Applets" tab. Add the system tray if it isn't there.
If you want the power manager to appear in the main menu, then you need to edit the desktop file, /usr/share/applications/xfce4-power-manager-settings.desktop. Remove or comment out the line that says "OnlyShowIn=XFCE;". It will then appear in the Preferences menu as "Power Manager".