Apprentice programmer doing journeyman task has need of a mentor....

How can I total the values in a grid column to a textbox on the form?

I have an order entry form with a grid. The last column is the extension (quantity * price). Below the grid I want a subtotal textbox to display the sum of the extension column.

This has to be a very common situation, but I haven't found any examples or discussions of the process anywhere.

I would greatly appreciate any explantions, examples or directions to articles describing what I need to do.

Thank You,
Neil Preston