I'm not sure what Edition 99 means. I would guess it means it was published in '99?
Amazon.com: Calculus Stewart Early Vectors
Aha. I just opened my book up, which would be that red/black one at the top there, and it says Copyright 1999, which is sort of misleading given that that Amazon link says May 2003 next to the book. (Plus, between you and me, I scoped out the MSC bookstore at my conference and saw the red/black book there in the MATH section.)
Perhaps I just had good luck on Amazon. This calc book, a bio book, and a chem book weren't hard purchases I suppose.
When in doubt, I'd just go with the newest edition available :s