[opensuse-packaging] Building RPMs for different versions of OS

Hi, Just for me to be sure (and not to miss something): Do I require an installation of every OS Version / Arch that I want to create packages for? As I just became the official package manager of a video client everybody knows (3letter) for SUSE Linux Versions, we'd like to offer packages of course for as many archs and versions as possible. But then again, my hardware availability (and budget to change this) are very limited (versions could be installed in virtual machines). Do I see this right or is there a 'way around' ? Dominique