Not sure if I missed something, but would this work too?
=TEXT(DATE(YEAR(A1),MONTH(A1)+1,DAY(A1)),"mmmm")
Edit.... Never mind, I figured it out. VoG's is good if you have the Text "march" in cell A1. If you have an actual date value in A1 though, it will not work. Mine would be the one for a date.