I'm sure a search (Google, Yahoo!, MSN, etc.) will turn up some good sources.
I used the books published by Microsoft and marked as "Learning Series" such
as the Step-By-Step books to study up for all of the exams - scored better
than 90% on all of them.
If you have access to Skillsoft (Thompson NetG) on-line courses, they are
also an excellent aid to making it through the tests. IIRC, the two Excel
2003 courses they offer damned near taught the test.
JLatham
MOS Master (Office 2003)