grid.getcolumnModel().setHidden(0,true) will be effected for column menu and not grid panel. In column menu u can enable or disable the column. How do we add or remove the column in grid panel dynamically?
I think this is what you are looking for http://www.extjs.com/forum/showthread.php?53009-Adding-removing-fields-and-columns
Make sure you look at post #37 in the thread as well.