How do you Highlight text within asp:textbox?

[Michael SL]

I have a large asp:textbox. I want to implement a "Find" function. It would be best if this can be done with a JavaScript (or some other method) totally at the client site without the server's knowledge

How do I
a) Highlight text within a textbox
b) Determine which text is highlighted (possibly by the user) within a textbox?

 

[Michael SL]

As a follow on question. If someone clicks in the textbox, how do you tell where in the textstream the click occurred?