Your registry has become corrupt. This is a bad thing.
Can you do a system restore from an earlier date? If you can, and then you can successfully install Google Earth, then all is well. Try this first.
If that fails, try the fine folks at www.HowToGeek.com, they are super friendly towards newbies with esoteric problems.
Lastly, you can do a Google search for "registry error 0x57", there is a little bit of documentation out there, but it's mostly tech-heavy.
To fix the registry error 0x57, you will probably need to make some changes to your registry. BACK UP YOUR REGISTRY BEFORE MODIFYING IT!