I have been using optical from my MacbookPro to my receiver powering some decent speakers for a while. Optical is always better.
You will need the Toslink 3.5mm to mini adaptor as previously stated.
You won't find that dollar part in any Circuit City, Best Buy, Radio Shack, PC Richards, etc.
No one will know what the hell you are talking about if you go there and ask either.
Also, none of their optical cables have that part included. Some use to have the adaptor inside.
If you don't have one order it online.