you have to be the administrator of that PC, maybe you're limited user. so check that.
right-click on My Computer then choose "manage" after that go to "local users and groups"
and check your user name is added to the administrator group or not. if not that's the problem
you have to be admin.
other wise you have to use the setup CD to add Arabic language, and by the way some of SP3
comes along with extra progs that don't allow multi-lang. so check that out. 'cause I don't remember
which program excalty that stops multi-lang option.