Return value to datagrid from Pop-up page

[Rattlesnake]

Hi,
I have a datagrid that is being used for data entry. I have a column called "Product". While adding a row , I want to allow the user to click on a button in the datagrid row which will pop-up a page that will have a list of all the available products(listed in a datagrid). He will select a product from the list.
What I want to know is how do I get this selected value back into a textbox in the datagrid in the parent form.
I can get the selected value in a session variable , but in the parent form how do assign this value to the texbox.

Note that the datagrid will multiple rows. How can I find the name of the textbox to which to return the value to.


Thanks