Qgis requires the GDAL 1.6, PROJ, GEOS, SQLite3, and UnixImageIO frameworks. Python support on Tiger requires a universal Python 2.5. Python support on Leopard uses the system Python 2.5. If you want to use the python.org Python in Qgis on Leopard, use the Tiger Qgis. GRASS support requires a full GRASS 6.4 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.
The Xcode project is now in the v1.1 source. I've removed the 1.0.x project because it's too much effort to keep it up to date for what will only now be possible bug fix updates in the 1.0 branch.
Qgis 1.1 is technically a release of the current development of Qgis, and is thus officially unsupported. But don't be afraid to try it.