KeyPress Event for asp TextBox

Hi. I've Grid in my page.
 
I have a text box. When I press a key in the textbox, based on the value it should filter the grid. My Boss want to do with the keypress event. For eg, when i press 'a', then the grid shouwld display the value starts with 'a'. When I press 'ab', it should display the value starts with ab.
 
Please help on this
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