I want to know whether I can legitimately apply for US citizenship in 2010, for myself, my wife and my two sons.

I and my family lived in Texas from June 1995 to December 2000. We first entered the country on visas and then applied for Green Cards.

We moved overseas in January 2001 on a work assignment, and obtained our Green Cards while living overseas, in December 2001. We returned to Texas in July 2006, bought a house, and have lived here continuously since then. I have been working for American companies continuously since June 1995 and have filed my US taxes each year since then. A brief timeline of our path to this point is given below:

June 1995 – Arrived in Texas with L1A visa. Sponsored by US employer.
March 1998 – Notice of action received (I485) Application to Adjust to Permanent Resident Status. Sponsored by same US employer.
Jan 2001 - Sent overseas to Brazil with family, by same US employer.
Dec 2001 – Issued US Permanent Residence Documents.
Mar 2002 – Issued Permits to Re-Enter the United States.
Sep 2004 – Issued renewed Permits to Re-Enter the United States.
Aug 2005 – Eldest son returned to the United States from Brazil, to attend full time college in Texas.
Jul 2006 – My wife, my younger son and I returned to the United States from Brazil, to live in Texas.
Aug 2006 - Bought house in Texas.
Jul 2008 – Changed US employers, still live and work in Texas.

I was told once by an immigration lawyer that I only needed to wait four years after returning to the US, before applying for citizenship. This instead of the usual five, because of our particular circumstances. Can anyone please shed some light? Thank you.