1.6r5 Dialog close button

My first question was going to be about proper CSS, but then I
realized I'd forgotten to include ui.dialog.css...but my second
question still stands. How do I disable/hide the close button? I
want to just have two button on the bottom to the effect of "Okay" and
"Cancel", but no close button. I tried using the "buttons" dialog
option with {"cancel": null} but this of course didn't work. Thoughts?