JQuery UI plugin not working in IE7?

I want to use the dialog box from this plugin, but it isn't compatible for IE7. When I run it in Internet Explorer's IE7 emulator, the dialog box renders weirdly. It's partly transparent, draggable/resizable doesn't work, and the title disappears.

As far as I know, the problem seems related to one (or both) of these:

1. The console says IE7 doesn't support "querySelectorAll". Is there a workaround for this?


2. If I render the page in Quirks document mode, everything works fine. Is there a way to force IE7 to render pages in Quirks mode? I've come across this, which suggests adding a comment before the doctype -- but I don't know how to do that in WordPress.

Any help would be greatly appreciated.