VCDGear (check versiontracker) can convert the .dat file into an .mpg. From there, I believe you can use Quicktime to do an "extract audio". I also believe it gives you a choice of formats to extract it in (.mov,.aif, etc.), but if it doesn't, you can use iTunes or QT itself to convert the .aif to .mp3.
Hope this helps.
P.S. I've found on OSX that you can sometimes just rename the xxx.dat file to xxx.mpg and it works. Other times, because of some header issue it doesn't. So you could always try that as well.