The preferences menu on Mac OS X is traditionally located under the application menu. In this quick tutorial we will learn how can we add fast this kind of option under the Mac application menu using REALbasic. Watch it, learn it, enjoy it!
To have your preferences menu appear under the application menu, all you have to do is make sure to create a super “PrefsMenuItem” of that menu, and REALbasic will take care of the rest. Go to Project Tab and click on MenuBar1. Now for example in Edit Menu Add Menu Item and name it Preferences. To display this submenu under the application menu go to it Super Property and enter there PrefsMenuItem.

Interesting would also be, how to store those preferences.
Alex
You can find in coments a solution given by Bob Keeney to do this.
http://realbasic.tutspolis.com/tutorials/cross-platform-code-in-realbasic/
But I will also create my own solution for it