I had a similar problem importing Sony EX 4 track files (these are Mpeg 2 in a wrapper) with Premiere 5.0. Adobe support could not help, I had to upgrade to 5.5 to get the imports to work.
Too bad i cannot upgrade beyond 5.5
Where exactly did you get the files?
A production company in my city gave the files to me, but I don't know with what software they are recorded.
When i check the files in Gspot (http://www.headbands.com/gspot/v26x/index.htm) they are OK, it founds two MPEG1 layer2 stereo audio pairs.
Also, if I play the files in VLC i can choose from Audio Track 1 and Track 2.