How to capture mouse click event on a button on web page?

Hi All,
can anyone tell me, how to capture the event, generated by clicking on a button
on a web page. suppose If I m sending an attachment with yahoo mail service, I
need to click on "Browse" button to choose the file, then system displays the
open dialog box "Choose File".

Now what I want is, to capture the event generated by clicking on "Browse"
button, so that i can display a custom dialog box to choose the file (instead of
system open dialog box "Choose File").

If any one can give me some sample code, then it will be more helpfull to me.

Thanks & Regards
Gautam S Yadav

<script language=javascript>
function getBrowser()
{
....
}
</script>

.
.
.

<buton onclick="getBrowser();>Browser</button>

Thanks for reply ! but I think my problem is different.

I am not talking about a page which is created by me. I am talking about the page which is coming from any server.
Can I capture the click event on "Browse" button on following page. ( I shown a .jpg file here) please find it from
following link.

URL



Thanks
Gautam