Celestia is a great free program which lets you "fly" through the solar system and even glaxies, exploring heavenly bodies. It also contains advanced features such as (for instance) tracking where the Cassini space probe is at the current time, by extrapolating it's orbit.

http://www.shatters.net/celestia

You will need a reasonably good computer/video card for this to run well.

VERY COOL!! thanks for the link...

Thanks, thats extremely cool !