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As you said it comes with Tiger. Besides that Im not sure what laws their are about sharing desktop backgrounds in operating systems.
 
maybe he doesnt have tiger...in which case i urge you to upgrade. if you do have tiger, go system preferences>desktop & Screensaver>Desktop tab>nature (from the list on the left).

it's the very first picture.

EDIT: you can also control click from the desktop and choose "change desktop background".

S
 
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