As post script to Rob's previous post, I highly recommend the the "Excel 2002
Visual Basic for Applications" writtten by Reed Jacobson, in the Microsoft
press Step By Step series or the "Excel 2003 Programming Inside Out" written
by Curtis Frye, Wayne Freeze and Felicia Buckingham, also published by
Microsoft Press.
The Inside Out book is a bit more in depth, but still a good beginner book,
and the Step by Step book is an excellent book for a classroom, as I've
taught many a class using that as the material. It will give you a thorough
understanding of the basic principals of programming and possibly show a cool
Excel trick or two to boot.