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I live in the USA, I put my home address, city, & state. It plugged the longitude & latitude info in automatically.

I tried that earlier, but the map doesn't work properly for me.

Infact, it's that very form I'm trying to find my longitude and latitude for.
 
I'm not in front of my Mac (I'm using my windoze machine at work), but on this version of Google Earth you can turn on the 'status bar' in the view menu and it shows you the lat and long of the pointer wherever you put it. The Mac version must have the same thing, or at least something analogous.

The other thing you can do is establish a placemark (pushpin) and get info on it.

Edit: checked on my Mac, it's the same. 'Status Bar' under the 'View' menu.
 
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