You want to create a motion menu, correct? Sounds like you’re using the 2.0 tryout.
From the Project panel alt-drag the video clip into an open menu to set it as the video background. If you have already animated your buttons in AE 6.5, then you’ll want to import the images (PSD?) that you used into the Library panel, then drag each one into your menu and align them to the buttons you animated in After Effects.
There’s more, but this should be enough to get you started. Look up “motion menu” in the online help and you should find more info that will help you piece it all together. And ask here if anything is unclear.
-Joe