In Excel 2003, when multiple cells are merged, it is hard to select each of the columns individually. Right clicking a selected row column will result in all the rows columns of the merged cell being selected. This typically causes a headache if you are trying to insert a column, hide a column, or change the column width.
Solution: To work around this, is to use the “Menu key”. (Its symbol is a small icon depicting a pointer hovering above a menu.) This way, no other columns will be selected.
Good news, this is fixed in Excel 2010.