Newer versions of PowerPoint have a “Create a Video” option under File, Save & Send -> File Types. I have used this feature before to publish the PowerPoint to YouTube. You have the option to record the slides with the specific timing between slides that you choose (simply clicking to the next slide). It is a fast way to create a video file with timing that matches the content of the presentation. I would suggest using this to create the video portion, pulling it into the Vegas timeline, then adding your soundtrack. Otherwise, you may need to convert each slide to a .jpg and add/stretch to get the desired timing.