Here is step by step procedure :
1. right click on the grid and edit it - see in the property sheet that grid has been selected
2. click column1 from the property sheet
3. click text1 under the column1
4. now click on the grid's column1 - the property sheet should still be showing text1 as selected
5. press to delete it.
6. drag a check box from toolbar and place it on the grid's column

Also set column's sparse property to .f.