By slideshow, are you referring to a video built in Vegas (or other app) or a DVD Architect picture compilation? If the former, drag your video onto the menu, name it, and set any other properties for the button. That's your "play once" button. If a DVD Architect picture compilation, well, then you should already have your play once button -- DVD Architect created it when you inserted the compilation.

For your looping version, you can do one of two things:

1. Copy the Play Once button and paste it onto the menu. Change the name, etc, and then double-click it. Go to the End Actions tab of the Properties window and change Destination to whatever you called this new button / media. Make you you do not set it to the Play Once media.

OR

2. Right-click the menu and choose Insert > Playlist. In the window that pops up, select your Play Once media and click Okay. Change the name, etc for this new button as you like. Then double-click it, go to the End Actions tab of the Properties window, and change Destination to whatever you called the Playlist.

Main difference is that, as far as I know, option #1 will add the media to your disc once, while the Playlist option will only add it once (meaning, it will use twice as much space).

Rob