Let's first see if it is the preferences. Go to System Preferences > Sound and see how it is set for out put. Plug the external speakers in (make sure they are not ones than need a special driver). Put the sound on line out. Make sure you selected the speaker port and not the microphone port. Let me know your results.
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If I need to I can play with one of my two MDD machines. Are you running 10.5.8?
Let's first see if it is the preferences. Go to System Preferences > Sound and see how it is set for out put. Plug the external speakers in (make sure they are not ones than need a special driver). Put the sound on line out. Make sure you selected the speaker port and not the microphone port. Let me know your results.