ajax watertextbox extender and javascript ?

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Hi, i have a textbox on the page. When the user clicks on a username in the
list to the right i use this javascript to insert their username into the
textbox.

function

setTextBoxText(text)
{
var textbox = window.document.getElementById("<%=touser.ClientID %>");
textbox.value = '';
textbox.value = text;
textbox.focus();
}
This works perfectly.

Then i tried to add a TextboxWatermarkExtender and now it does not work
anymore, the initial text in the textbox (set by the watermark extender) gets
erased, but the username does not show up, it just turns blank and focus is
set on the textbox. Is there anyway to fix that?

Patrick