The last time I went looking for a desktop GIS application for my Mac all I found was the beast of a system that is GRASS (it looked so powerful, but yet so far beyond my reach to properly grasp).
I began by exporting the MapInfo file as an ESRI shapefile using the trial version of MapInfo running on my Mac using Virtual PC. Both Quantum GIS and uDig then opened this file with no problems:
Now the fun begins: I’ve got some “ZIP code in polygon” magic to perform and my next step is to see which tool supports this sort of thing best. Stay tuned.
Update: There’s also Thuban.