You can hide the individual sheets but I don't think you can password protect them from being viewed. You can password protect the workbook.

I may be wrong. I've searched the net and find some links...
http://www.ehow.com/how_8228429_pass...cel-sheet.html
http://office.microsoft.com/en-us/ex...010078580.aspx

The above may only not allow changing data but I don't know if it keeps others from viewing the data.