Using Variable in gotoAndPlay!?! NEED HELP ASAP!

Hello everyone,
Im working on a flash menu right now and I wan to create a dynamic gotoAndPlay. but I need to insert a variable into the target path right now here is what Im doing.

 MyVar="FirstMC";
_root.Nav.MyVar.gotoAndPlay("out");

and right now Flash doesn know what to do with it… I would like to make this variable global also which is nothing more than throwing the _global command before my variable right? Anyway I need help fast! The project deadline is fast approaching!
Thanks!
Fidelity88