All GPS modules output NMEA0183, which is simply a bunch of ASCII-encoded serial port data. 4800 (or sometimes 9600) baud, 8N1. There are a lot of sentences in that protocol but the one containing lat/long is the critical one (obviously).
In fact, if the voltages are compatible you can simply hook the GPS output to your PC serial port, start up Hyperterminal, and watch the NMEA sentences go by.
The MSSP module can read it and it's also possible to bit-bang the interface. Being ASCII you will need to write code to interpret it as binary-encoded numbers to work with.
Some modules have proprietary modes you can invoke with a specific command sent to the module. Many are serial-encoded binary data which is faster than ASCII. These modes may have more specific GPS data than offered through the NMEA0183 standard sentences. Some GPSes even have commands to reconfigure the receiver mode to something more appropriate to what you need (walking vs flying).
Also proprietary sentences may be used with NMEA mode to change the frequency of messages, the baud rate, etc. The GPS will still output NMEA0183 data.