I don't think either ASP or PHP had in mind the possibility of the exchange of information between languages. I believe both saves session data in local files, so theoretically you could convert one into the other if you were perfectly knoledgeable on both you could make a converter, which would be tricky, and possibly too slow for web applications.
what you could do is transfer the desired data to form the PHP page to the ASP one (and vice-versa) via get or post.
I won't assure you now, but another option is to make an fopen() call to execute an asp/php file and request/input data via get, like:
fopen ('http://localhost/request_data.asp?id=777');
fopen ('http://localhost/input_data.asp?data1=1&data2=2');
except it's not going to be easy either, IF it works