Can’t Crack Google?

I have been working at SEO for over 6 months now and have good results in Yahoo and MSN ranking on the first page for many of my important keywords, but I still don’t even show up in Google results at all — its like we don’t exist for Google! Does anyone have any insight as to why this might be the case? We must be doing something right to get the improved rankings on other search engines, I think, but I just can’t figure out what we need to do to get into Googles results (we have a Google page rank of 3). Any advice?

Laura