http://www.videohelp.com/tools?tool=DGPulldown
http://neuron2.net/dgpulldown/dgpulldown.html
or use one of these programs to convert the pal dvd to ntsc and then rip the audio from that conversion to sync up to your ntsc video
I've also used VSO ConvertXtoDVD v2.1.5.173 to convert pal to ntsc. Then you could just use a dvdrip program to extract just the 5.1 audio
excellent guides found here http://www.videohelp.com/guides.php?howtoselect=4;41#4;41
overall I think dgpulldown might be the easiest way to do it..