To put a combo in grid cell

[SAKHI_SUPER1]

I am using vb.net 2003 and infragistics tools. I am using ultragrid for sales invoice. Now the grid is working for entering values in cells manually. Whereas, I want to put a combobox or a dropdown list in cells of product code column so that user can select from the list. I just could'nt put that combo or dropdown list in gridcell. Any code for that will be highly appreciated. Thanks