> What is the difference between a MAC-created and a
> Windows-created file with the same MIDI data?

None.  

MIDI files (as long as they are standard) transfer from Macs to 
peecees and back without problems as long as

  * the stupid mac type is MIDI
  * the stupid peecee extension is mid
  * the transfer is binary
  * you actually transfer the data fork (mac -> pc)

Byte swapping (ie, big/low-endianness) is _not_ an issue since
MIDI files consist of bytes only.

Standard compliance, however, may be a problem. Programs are 
supposed to skip unrecognized meta messages, but for system and
channel messages the picture is a bit less clear since they 
haven't been anticipated to change.  Meantime, however, port
and cable messages were added, which (if they are actually used)
may confuse older programs--and which definitely would break the
csound parser.  

Some csound binaries seem to have a bug with respect to program
changes.  In particular the binary that comes with the IRIX 
version of Jean Piche's (and Alex Burton's) Cecilia.  Other than
that, however, it should parse everything ok.


Again, if you encounter a file that doesn't work with Csound, 
feel free to strip it down to ideally only the offending message
and post it.