Izarc as is don't seem to be able to create context menus in Vista. 7Zip works great, although its handling of rar files is not perfect (multiple rars for example, if any of them is missing, 7 zip will unrar as much as it can and then just exit without any warning, or if you start unrar from .r01 file instead of .rar, it will just unrar single file, no warning, no popup, no logic...)