I am running Lubuntu 11.10. By default the main menu is bound to Alt+F1 (A-F1) which works. Here is the relevant code from ~/.config/openbox/lubuntu-rc.xml

<keybind key="A-F1">

  <action name="Execute">

    <command>lxpanelctl menu</command>

  </action>

</keybind>

This works. When I hit Alt+F1, I can see the start menu.

If I change the keys to "Windows key + M" (W-m), I can pull up the start menu using Win+M

<keybind key="W-m">

  <action name="Execute">

    <command>lxpanelctl menu</command>

  </action>

</keybind>

However, I cannot bind the start menu to the Windows key alone. If I try replacing "W-m" by "W", the "W" alphabet key gets bound to the start menu. If I try "W-" nothing happens, I have tried the "Super" option too but to no avail.

How can I bind the Lubuntu main menu to the windows Key?

I have been through some relevant lubuntu questions, like this one, which tries to do the opposite.
How do I unbind Super key from menu in Lubuntu