How to Create Tooltip on Code Behind for "TAB Button"

Question

Hi Friends......,

I Need to Create a Tooltip on code behind when tab button is clicked it moves from one       "text box A" to "text box B" . when cursor is in textbox B tool tip needs to show "Tooltip Message"........

Is There any Code Plz Let Me Know  ASAP

Regards.....,

R.V.Rajagopalan