I have creating a menu with buttons in Photoshop, such as Play, Scene Selection, etc. I want to be able activate those buttons in Encore. How do I accomplish this?

Assuming every button is on a separate layer in your photoshop menu file, you have to select each button in turn and select 'convert to button' . You can then link each button in turn to chapter points in timelines or to menus as required.

it is pretty simple,
here is quick tutorial

Adobe - tutorial : Create a DVD menu in Adobe Photoshop (http://www.adobe.com/designcenter/encore/articles/enc15menu.html)