Use the Monster Cable linked to previously to connect to a Toslink 'optical in' on your receiver from the 'optical out' mini-plug on your MBP. My Denon lets me assign the optical inputs using a video menu, so now you have sound going in and just have to select the source (by whatever means your receiver uses).
Now that you've got sound, you want a picture! Use a DVI to HDMI cable or a DVI to DVI cable with a DVI to HDMI adapter. Plug into your receiver. If you're like me, you have all audio and video going through the receiver with a single 'monitor output' going to the HDMI (or, on some TVs, DVI) input on your TV - all your 'switching' is done at the receiver instead of multiple inputs on the TV. Just make sure that the DVI-DVI or DVI-HDMI cable that you get matches the DVI out port on your MBP.
You might be able to find both cables at a local Best Buy or you may want to call
Crutchfield and they may have the cables you need in stock or may be able to tell you which Monster cables you need...
...and although Monster has almost taken over the market there are other manufacturers but they're becoming more difficult to find... just don't buy the $200 'reference' cables to connect your computer to your TV!!! In fact...
...if you don't have all sorts of DVI cables just lying about, you might want to save some bucks and buy Apple's $19
Apple DVI to Video Adapter that allows you to just use a single composite or s-video cable.
20" 2GHz Intel Core Duo iMac 2Gb RAM 250Gb, G4 Dual 1 GHz PM & 12" 867 MHz PB, Mac OS X (10.4.6) 2 MacBook Pro Intel Core Duo 2 Gb RAM 100Gb 7200 RPM HD