Ashish,

>1) How to reize the combo box ?

You can't. The size of the combo is controlled by the size of the gird column and row.

>2) If I want to use combo box builder to populate the combox box how can I do that ?

First put the combo in the form. Use the builder. The select the combo and use Ctrl-C to copy it. Now click on the grid, right click and choose edit, then click in the column you want and use Ctrl-V to paste it in. Lastly delete the combo form the form.