I can't check this because Ctrl+Alt+Tab doesn't seem to do anything on my machine, but the code would probably be:
Rwin & Tab::Send, ^!{Tab}
If this doesn't work, check first with either SoundBeep, 500, 500 or a normal character. If the SoundBeep, 500, 500 or normal character in e.g. Notepad doesn't work either, you might have to run AutoHotKey in Admin mode (Windows 8 issue).
The alternative that Aaron Miller came up with should be:
RWin & Tab::Send {Ctrl Down}{Alt Down}{Tab}{Alt Up}{Ctrl Up}
But as said again, test FIRST if AutoHotKey does work in Windows 8 with something simple like e::a . There is a good chance it does NOT, unless you run it with Admin rights (right click run as...)
I realize why Ctrl+Alt+Tab doesn't work on my machine. I disabled Flip 3D!