Okay, so from reading the message board, somebody suggested VLC Player, which I just downloaded, and it worked great. It also played my .mts files, which means I won't have to bother converting all of my videos.
Still, it would be nice for WMP to work.
I downloaded a few videos from my HD digital camcorder to my computer and used the included software (ImageMixer 3 SE Ver. 5) to create both an MPEG-2 file and a DVD. When I play either of these with Windows Media Player 11, I can see the video just fine, but there is no audio. My laptop runs Windows XP Professional Version 2002 Service Pack 3.
I can get the DVD to play with sound when I use CyberLink PowerDVD, a DVD software program that I assume came with my laptop. Also, the DVD played just fine with sound when I played it on my wife's Mac laptop.
So, basically, it seems like the problem is with WMP.
When I first played the DVD on my PC laptop using PowerDVD, I had to change the region from Region Free to Region One as the DVD was recorded using Region One. Perhaps there is a similar region setting within WMP that I need to change? I have looked for it, but could not find it.
I would also be happy to take recommendations on other media players in place of WMP, if someone thinks that would be an easy solution. However, it would be nice for WMP to work because my parents would likely try to use that if they tried to play the DVD on their computer.
PS - If there is another thread that clearly answers my question, please just send me the link to that thread. I tried to search for one, but had no luck.