If your web site has good rankings on Yahoo, MSN and other search engines but not on Google, it's likely that your web site has been put into Google's sandbox.
What is Google's sandbox?
In general, brand-new web sites with new domain names need about 6 - 8 months to get top rankings on Google.
The usual process is that Google indexes the new web site, lists it for some less important queries and then the web pages drop from the search engine result pages for several months. Although other search engines work fine, Google doesn't list the web site, sometimes not even for the company name.
If you have a brand-new web site, don't worry about this behavior. You are not doing anything wrong. Google seems to delay the inclusion of new web sites. This phenomenon is called the Google sandbox.