Video Editing Software Question. Any Experts?

I have never done video editing before, but have recently begun using Sony Vegas Movie Studio HD 9 for PC. I am having a problem with the sound going out of synch with the video. The original files (stored as QuickTime movie files) on my hard drive are fine, but the sound goes out of synch (about a half second late) shortly after I upload them to the Project Media area of the software. When looking at the video and audio tracks on the timeline, there is no visible shift.

I sent a request to the Sony help desk five days ago, but haven't gotten anything from them other than an acknowledgement that they received it, which is pretty crappy customer service, IMO.

Any help or suggestions would be greatly appreciated. This is driving me nuts.

 

Thanks!