Even before you are done with the video, you probably need to start planning the event to unveil. Ideally, you will invite your mom's friends and family, so you probably want to let them know in advance enough so they can plan travel if necessary.
In terms of tactical things about the day, here are some things to consider:
You need a TV with a DVD player hooked up. Ideally this is large enough to be viewable by many folks at once.
You want a room with seating to accomodate all your guests.
You will want to do a dry run so you are comfortable with the controls on the DVD player you use. One tip - set the settings on the DVD you create to automatically play from one chapter to the next without you having to select each chapter. I also suggest you have the DVD go automatically into playing the first chapter when you insert it. If you have to go to a menu first, this may kill the surprise effect.
Make several copies of the DVD to bring with you to the unveiling. Some of the guests may want one. It is also a good backup if the one you have doesn't want to play. You can also potentially save all the individual pictures as .JPG files on those disks, which is a great way to backup all those priceless family photos you have taken the time to scan.