Michael
Make that Format>Cells>Protection and uncheck the "locked" box.
IGA
By default all cells are locked when sheet protection is enabled.
To lock just a few, hit CTRL + A(twice in 2003) to select all cells.
Format>Cells>Protection. Uncheck "locked" and OK.
Now select just the cells you want locked and check the "locked" box.
Sheet Protection must be enabled as Michael points out.
Note: Tools>Customize>Commands>Format. Scroll down until you find a padlock
icon.
Drag that to your Toolbar and use it to lock and unlock cells before
protecting sheet.
Gord Dibben Excel MVP