HDMI Audio Out Problems

I've been trying to link my M1530 to my Samsung HD LCD TV via HDMI output. I've got the video under control, but am having trouble geting audio to consistently play through my TV speakers. By setting HDMI as the default playback device in Sound settings (and sometimes rebooting - still not sure what effect that does or doens't have), I've managed to get mp3 audio to consistently play through the TV and also system sounds. However, that's not the case when playing a DVD rip (from HDD) in Windows Media Player for Vista. The audio from the DVD will play fine through the laptop speakers when the default playback device is set as such, but if I change it to HDMI and reboot (and keep in mind, mp3 audio will play on the TV immediately before I try the DVD), I get no sound at all. The kicker is that I had it working once, but received a phone call and stopped the video and then went to look at the settings, then tried it again and it didn't work anymore. Any suggestions as to what might be the problem?

 

FYI, incase anyone else is having this problem. I tried another DVD player software (Cyberlink PowerDVD) and it worked fine. That means the problem is with Windows Media Player or the codec it uses. I'll try to figure out more, because I don't really want to waste another 500mb of space when WMP should play DVDs just fine and is already installed.