Welcome, Gertrude. I agree that Civ 4 is the best Fiv and you will find a lot of people who feel that same way here.
Yes with Beyond The Sword....no finer game in the series!!
That being said, I still play CIV II and my favorite feature of this series is from CIV II that being the ability to not only trade goods but also sending food caravans and the ability to help finish the Production of a Wonder.