»api«

Until today, the Yahoo APIs were available only for non-commercial use unless you applied for an exception. The concept of commercial and non-commercial has gone away and exceptions are no longer necessary in most cases.

You can now build Mashups and use our Maps for personal or business use as long as the applications are free of charge and under the rate limit, link to Yahoo! Maps or Driving Directions to your heart’s content or include advertising on the same page or site where you display Yahoo! Maps.

... Yahoo! Maps: You don't have to ask!

Some thoughts about the possibilities of API only services and Web 2 here at Joseph Scott's Blog:

"With open and usable APIs others are free to create entirely new 'products' by mix and matching APIs from various sources. This is great because it allows so many people to be involved in the process, not just the companies who came up with the original services. The more people involved, the bigger the pool of imagination from which new products and services can emerge."

Joseph Scott's Blog » API Only Services?

Bad News first: The Earth download page is down. This is, what the Google Earth Page currently says:

"Thanks for your interest in Google Earth, but we're sorry we can't offer you a download right now. As you know, Google Earth is in beta, and we're still building out our ability to take on new users. ..."

(Google Earth - Temporarily Closed)

So, leave the passive role of the spectator and build your own interActive maps using the freshly released Google Maps API:

http://www.google.com/apis/maps/