I put the DICE unit in my GS300 last summer. Install was a breeze. Follow the well-known directions on this forum to take the radio out. Once it's out the connectors on the DICE unit plug right in, and then put it all back. Pretty straight forward.
I ended up putting the actual DICE "box" in the glove compartment (allowing me to easily run the cable behind the dash). I keep the iPod plugged in and put that in the glove compartment too - out of sight. This way, I can use the steering wheel or touch screen controls to navigate my music, and if I need do, the cable is long enough that I can get the iPod out of the glove compartment and use that too.
How much did it cost? Can you post some pics?