You can have as many OSes so long as you have space on your hard drive. If you have free space on your hard drive you can install any distro you want but **don't install the bootloader**. Once you finish installing the new distro, you would have to log into SuSE and manually add the new OS entry into the grub menu file. If you don't have any free space left on the hard drive, you may have to resize the partitions on the disc.
If you don't want to do that, then the easiest way is to get another hard drive, plug it into your PC and install the OS on the other drive. In that you case, you would just have to alter the grub menu file to boot the new OS.