Using jQuery UI's dialog to pop up a form, I could not do this for some reason. Here is my code to set input focus in a dialog.
// In event handler
$('#mydialog').open();
$('#myinput').get(0).focus();
And nothing! I tried with many dialog options, and the only thing I could do to make it work, was to eliminate the dialog.
The only thing I can figure is that the dialog itself is setting focus, or blurring my focus. So I fixed this by delaying the focus call using a timer.
// In event handler
$('#mydialog').open();
setTimeout("$('#myinput').get(0).focus();", 500);
Note, times less than 200 ms were not reliable.