How to access the value of a Texbox column(Template field) in gridview

[Yog]

Hi,

How to access the value of a Texbox column(Template field) in gridview
and to update a column next to it in the Gridview...!

Example:Let's say there are four columns Product,Cost,Quantity
Required(Textbox type template field in Gridview) and Total...!

Totla shud get updated by Cost*QuantityRequired as soon as the user
focuses on next row in the gridview.....!

Hope I m clear....pls tell the sol. (its a bit urgent...!)

Thanks in advance,
Yogesh