In my opinion, there is no point in using the border-radius property as it is CSS3 style......CSS3 is not out or finalised yet and not enough browsers support it, so if someone was using IE then they would see with square corners rather than te rounded.
Best bet is to use a graphic as suggested, but i believe there is also a mod called nifty zen which uses javascript and css to create rounded corners....but i havnt used it so not sure how good it really is



