you need to create an image in PhotoShop with rounded edges and put in on the button. that the only way.
All right brain, you don't like me and I don't like you, but let's just do this one thing so I can get back to killing you with beer.<br /> <br />- Homer Simpson
That's not the only way, but that is by far the easiest way. Otherwise you have dig deep into the Button UI and over ride the paint() to paint it how you want to. I would use an image.