The Mac App Store won't run on Mac OS X 10.6.5 or earlier. You posted to the 10.3.x or earlier forum. However some versions of iTunes will, but it is unknown at this time if any version that will run on those operating systems is still able to access to the iTunes Music Store for purchases. Are you really running Mac OS X 10.3.x or earlier? Go to Apple menu -> About this Mac to determine that. Once we known your operating system version, or iTunes version, we can ask your thread be redirected to someone who can help.