Download and install AutoHotkey.
Create a text file called AltGrToMenuKey.ahk (or any other file name ending in .ahk) in any folder of your liking, and put only this line in it:
LControl & RAlt::Send {AppsKey}
Double click the AltGrToMenuKey.ahk file.
Put a shortcut to the AltGrToMenuKey.ahk file in your Startup folder in Windows so it is started whenever you restart your computer. (This folder is normally placed at C:\Users\<your user name>\AppData\Roaming\Microsoft\Windows\Start Menu\Programs\Startup in Windows 7.)
I just tested it and it works excellently on my Windows 7 computer.
Instead of downloading AutoHotkey and setting up the script, I have also made a compiled .exe version that can be downloaded and run as it is. Just place it anywhere you want, run it and make a shortcut to it in your Startup folder as in step 4 above. Of course you would need to trust me in that it does not contain any maleficent code. If not, just use the 4 steps above instead. AutoHotkey itself is known and trusted.
It should be noted that while this script is running you can still achieve the Alt Gr effect by pressing Ctrl+Alt. That could be handy should you ever need the special characters or keyboard shortcuts that Alt Gr normally gives access to. Ctrl+Alt works essentially the same as Alt Gr, but this script sees the difference and only invokes the menu key if the Alt Gr key is pressed.
