Is it possible to get an item in a menu to be "blank". So its only a way to get a drop duwn menu. It should not be clickable.

I don't know of an "easy" way to do this with the existing menus. If what you want to do, though, is provide some separation between a couple of tabs, you could add a padding attribute to the one that you want to separate. If you are using the DNN Nav Menu, each item has a unique class.

No thats not what i meant.
Lets say that i have this menustructure:

Home
...Welcome
...Introduction
Classes
...Teachers
...Schedule


I dont want 'Home' and 'Classes' to be clickable. I want all the content and info to be in the subpages. I just want these two to act as an item for the drop down menu.

Thanks!

You need to 'disable' the pages you don't want clickable. Go to Edit Page Settings, expand Advanced Settings and tick Disabled. Of course, you don't really want to disable the Home page. Should you need to edit these pages in the future, you can do so via Admin > Pages.