Microsoft: Excel Security Take Charge and Stay Secure: Protect Your Documents with Passwords.
http://www.microsoft.com/insider/articles/OfficeSecurity3.asp
Protect Excel Worksheets Using the Protection Object to Protect Your Worksheets.
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnexcl2k2/html/odc_xlwebProtSht.asp
Introduction to Excel 2000 Library of Excel 2000 tutorials.
http://support.memphis.edu/train/software_links/excel2000/excel1.html
Excel's Dirty Little Secret Spreadsheet passwords can be foiled by simply copying and pasting.
http://www.nwfusion.com/news/2001/1217excel.html