The current way to get interaction data out is to navigate to
a particular model and then select the option:
File->Export->Export to SIF...
This will create a Cytoscape-compatible SIF file with
a line for each interaction. This is an old function,
and the node names used in the file can get pretty
obtuse. Here is a previous posting that discusses how
to parse out the node names that show up in this file:
While this approach does not describe how to extract the info
from the .btp file directly, I hope this does what you need.