There is another way ..where you dont need to change anything in your mpqs...
Allow Local Files has to be activated therefore
Windows Registry Editor Version 5.00
[HKEY_CURRENT_USER\Software\Blizzard Entertainment\Warcraft III]
"Allow Local Files"=dword:00000001
save that code to an *.txt-file rename it to *.reg and import it (doubleclick).
then put the menubackground you want to use in the folder:
"%Your Warcraft III Directory%\UI\glues\MainMenu\"
and rename it to "mainmenu3d_exp.mdx"
Add that Possibility to your Tutorial
I also added some Backgrounds i already extracted..as attachment
some miss though (e.g. arthas and rexxar)
maybe add an complete pack to your Tutorial
my favorite: Lich ....just roxx!