Or if you don't want to use RegisterStartupScript, you still can use this method.
'copy this code in your before you <html> tag.
<script language="JavaScript">
function cmdFocus()
{
document.all('textbox1').focus();
return false;
}
</script>
'After that just include this statement into your <body> tag.
onload="cmdFocus()"
'so your page should look like this
<script language="
vb" runat="server">
....anything in your application....
</script>
<script language="JavaScript">
function cmdFocus()
{
document.all('textbox1').focus();
return false;
}
</script>
<html>
.......
<body onload="cmdFocus()">
<form runat="server">
.....
<asp:textbox id="textbox1" runat="server"/>
.....
</form>
</body>
</html>
-----------------------------
Hope this will help you since it works to me