Does anyone know of a jQuery plugin or something that will get rounded corners working in IE 7 and 8?
Not without lots of extra markup. You can look forward though to CSS support for border radius in IE9
Is it acceptable to the OP for the plugin to add extra elements to the page on all web browsers, if that's the only reasonable way for IE to enjoy that which other web browsers take for granted?
My understanding of this plugin is that it only extends existing border-radius support. Am I reading this wrong?
Try http://css3pie.com/ I used this recently covers: border radius, box shadow and a few other selectors and IE never looked better.
http://css3pie.com/ is probably the best implementation I've seen. Quick and light.
Note--it does not work well on animated elements.