Qgis requires the GDAL, PROJ, GEOS, SQLite3, and UnixImageIO frameworks. Python support on Tiger requires a universal Python 2.5. Python support on Leopard uses the system's Python 2.5. GRASS support requires a full GRASS 6.3 application (and any extra frameworks it needs). See the Qgis website for more information about Qgis.
A universal gpsbabel is included for use with the GPS Import plugin. Qgis should automatically find it.
Note: If you prefer python.org's Python on Leopard, install that and run the Tiger Qgis on Leopard. If you use the Leopard Qgis, but have the python.org python installed, Qgis will get confused and the Python features will be disabled.
