I'm not sure if anyone has done this yet in a semi-permanent fashion, but I got really bored of using my webplayer at bedside (I never sleep, what was I thinking?), so I mounted my webplayer in the car today.
I've got a 1990 Toyota Celica with 185,000 miles so I figured who cares if I F*** it up. Anyway, I started by removing the glove box. This allows the webplayer to recess into the passenger side console. It mounts to the top of the inside chassis for the glovebox. Two giant wire ties pulled VERY tight and wrapping completely around the body of the webplayer hold it in place. Believe me this puppy is TIGHT. Removing the glovebox and installing the webplayer here has actually increased legroom on the passenger side. Legroom was a concern of mine when I first decided to mount on the passenger side.
The webplayer is still powered by the original power supply. The power supply is plugged into a 150W power inverter all stuffed behind the center console and out of the way. The audio goes directly into the preamp inputs of my SONY full-DIN EQ. This gives me graphic control and splits the sound to my two amps in the trunk. It sounds GREAT. Much better than I expected.
My webplayer already had a 4.3GB hard drive installed, so I've got plenty of space for mp3's. To get them on the unit I use the SMC USB adapter. The webplayer runs full win98se, and when I'm plugged into my LAN (gotta have the car close enough to the house to plug the RJ-45 cable in, looks really funny) I can even surf the web from my driveway.
So far I have not had ANY issues with the USB ethernet adapter at all. I just finished copying 800+ megs of mp3's onto the webplayer at once.
Next I have to figure out how to hook it up to my garmin GPS-12 for navigation :)