Microphone input (G5)

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I'm trying to get a microphone I bought to work on my G5 but it  
doesn't seem to register in the system preferences.  It works fine on  
my friends PC computer.  I've looked around on the net and heard that  
Apple provide poor quality audio input ports that won't provide  
enough power to support non-powered microphones.

If this is the case I'd appreciate some guidance.  I'm more after  
economy rather than quality.

Thankyou
Ruben A. Franke