Welcome to the Apple Discussions. A number of users have reported problems with syncing the music to the slideshow. If you find that's the case you might consider creating the slideshow in iDVD using the stills. Here's how:
1 - create an album of the photos you want and arrange them in the order you want.
2 - select them and use the same Share->Send to iDVD menu option.l
3 - once the photos have been imported into iDVD you can assign the transition to use between photos and set the music to use via the Media/Music pane.
Click to view full size
*NOTE: the Ken Burns effect in iPhoto is not available in iDVD.*
4 - when you've complete the project use the File->Save as Disk Image menu option to create a disk image of the project. This will separate the encoding of the project from the burning process.
Click to view full size
5 - mount the disk image by double clicking on it and then launch DVD Player to preview your project.
6 - If it plays as intended with DVD Player then burn to disc with Disk Utility or Tosat at the slowest speed available to assure the best burn quality. Always use top quality media: Verbatium, Maxell or Taiyo Yuden DVD-R are the most recommended in these forums.