Yes, do all your menus in the same IVR script.
If I have a menu and submenus I usually add 10 for the key pressed in main menu and 1 for the key pressed in submenu to the IVR_return variable.
So if they first press 2 and then 3 I add 20+3.
This is only needed if you need to go back to the main menu from your sub menu, otherwise they could be different scrips.
"Trying is the first step to failure..." - Homer