This site has some good ideas and has some Unity3d resources:
This dude has a tutorial that explains how to take a mesh from Google Earth, import it into Sketch Up and then import that into Unity3d:
Here is a website talking about approaching Unity3d from a Flash developer's perspective:
There is indeed a z at the end of the title of this website and that is why it will succeed. Seriously though, there are a ton of great links on this page:
Funny thing, I randomly met the man who invented Wikipedia. He told me what the next incarnation of Wikipedia would be, and it was such a tongue twister I forgot it and haven't seen it developed yet. Thank goodness. Anyway, there is a Unity 3d wiki called UnifyWiki, it's ahsum:
Last but not least, some video tutorials from learnmesilly.com:
Wish me luck.