I just finished installing SIRIUS radio in my dad's GS300 as his father's day present. (I'm not going to be here this weekend so its and early gift)
I ran the wire from the antenna around the window edge down to the trunk. I went through the trunk and, after removing the rear seats, went through the trunk and tucked the wire under the footsills along the pass. doors. I then took the wire and went up through the hole i drilled into the glovebox and then into the unit. With the power cord, I ran the cord theough the hole in the glovebox and then into the SIRIUS unit. I then ran the other end of it along the center console and under the center console storage box. I punched out the square piece from the back of the storage compartment and then ran the power cord into the 2nd power source. All the wires are hidden and it really looks good. Plus, the SIRIUS unit can be locked up when the car is parked b/c it is hidden and in the glove box. And eventhough the driver can't mess w/ the buttons on the unit, the remote control can still be used, so there is no point in being able to reach the unit itself.
Anyways, here is the end result:

 

2nd pic (from the drivers seat):

 

3rd pic of the power cord going through the center console storage box: