Yes, you can. Go to "objects" (next to "video&audio" and "backgrounds"). Then import the jpegs you want as buttons. You can now drag them to the menu and use them as buttons. Just rightclick them and link them to the audio.

I would also suggest changing the standard dvd-lab purple color of the buttons. You can do that by changing the colors in the "map" menu, it's on the right of your dvd-lab screen under properties. Just change the colors and run "menu > simulate" to see if you like the effect.