How to protect excel sheet and formulas

Hi Friends, I want to lock my excel file so no one can view or edit formulas, VB functions or manually delete or modify worksheet data,
I have 3 sheets Input, Inventory and Stock, If I enter data in input it automatically add to inventory sheet and calculate running total in stock sheet. once its done the input sheet gets blank for next data entry,
I tried to protect cells containing formula and assign password to sheet but when I enter data in Input sheet it wont write to inventory sheet and also doesn't get blank.

Pls Help....

for others, cross posted:
http://www.vbaexpress.com/forum/showthread.php?47949-How-to-protect-excel-sheet-and-formulas
http://www.excelforum.com/excel-pro...-how-to-protect-excel-sheet-and-formulas.html

for vivek_vx, some light reading:http://www.excelguru.ca/content.php?184