if your using excel 2007
highlight the column you wish to protect. go to "Home" tab in group
"Cells" click on "format" then click "lock cell" click on "format" again then
click "Protect Sheet"
if your using excel 2003
highlight the column you wish to protect. Click on "Format" the click on
"Protection" Tab then click on "Locked" click "OK". Click on
Tools/Protection/Protect Sheet
hope this helps