Forget about the bending drywall method, unless you are going to have very lazy, mild arches. Even if you do go this route, you will need special flexible corner bead. If I were going to do this I would use the pre-fab arches available at Outwater plastics, the people who make 'em at www.outwater.com see: http://www.archpro.com/arch_passages01.htm for their selection. I have ordered many many things from them over the years and I haven't been dissapointed yet with the price, quality or selection.