the other solution that I have seen is putting a div inside each of those th's and applying the resizable() to that. But that was for the same firefox bug, dunno if it will help with IE7.
As a possible aside, IE is very finicky about constructing tables using innerHTML - yours renders fine in IE8, but if the above doesn't work, maybe consider using proper DOM methods?
(and why does it have to be made that way, anyway..? there's nothing dynamic getting added - you could just as easily hardcode it and hide/show it)