Here are the steps to add background music to PowerPoint:
1. Display slide 1.
2. Click Insert -> Movies and Sounds -> Sound from File, locate the folder that contains the sound file that you want, and then double-click the sound file.
3. When a message is displayed, click Automatically.
4. Right click the sound icon, and then click Custom Animation.
5. In the Custom Animation task pane, click the arrow on the selected item in the Custom Animation list, and then click Effect Options. Tick from beginning under the start playing, at the stop playing option tick after slides and input the 999.
After these, the music you add can be played all over the slides.
Then, you can convert the presentation to avi with PPT to dvd software, such as Wondershare PPT2DVD (http://www.ppt-to-dvd.com#110 )
Best wishes.