Excel should protect content when files are password protected.

[CardPunch]

Even when I password-protect my Excel workbooks, sensitive data shows up as
plain text in the Google desktop search. It is very dangerous to give users
the false sense of password protected security when the underlying data
remains plainly visible. Password-protecting a workbook should result in
encrypted content that cannot be easily searched and displayed.

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http://www.microsoft.com/office/com...f9b9cc7&dg=microsoft.public.excel.crashesgpfs

 

[Duke Carey]

In XL2002 (and presumably 2003, too), using File->Save As allows you to
encrypt the file. In the File - Save As dialog look under Tools->General
Options->Advanced