Video and Audio don't sink when 2 .avi files are combined.

[Steven Vollom]

Normally when I join to .avi files, they video and audio remain in sink, 
nonetheless, not this time.  The one noticable difference between this 
joining is that usually, two parts of a film are contiguous.  The second part 
starts where the first part left off.  

This time, the movie credits are included on part II as well.  I am not sure, 
but this is the only thing I can see that is different from the norm.  If 
that is the cause of the problem, how can I fix it?  TIA.

Steven