On a Mac, you hold down the Command key. (And on a PC, it's the Ctrl key, not the Alt, by the way )
I don't know which instructions you're working with, but I do get it right in my books, for what it's worth!
Welcome to the forum.
It sounds like you are running up against PrE's default to do a Ripple Edit, when you want an Insert Edit. The modifier key to use to toggle between Ripple and Insert, is Ctrl (on a PC, which should translate to the Cmd key on the mac). If the Ctrl key is held down, then the editing process becomes an Insert Edit.
Let us know if that works, and good luck,
[Edit] Steve, thanks for affirming that it IS the Cmd key on the Mac.
Message was edited by: Bill Hunt