Hi Murls,
You CAN open an InfoPath on a Mac. No, not directly, but as Matt mentioned, "browser enabled" forms which is a new feature of InfoPath 2007. If you have workflow that requires Macs, it works. I have tested in both Safari and Firefox on the Mac. The out of the box samples includesd with InfoPath 2007 will open fine on the Mac. One thing i did notice is that the Mac does not appear to support rich text fields, you can enter data into them, you just can't format as rich text.