Been done several times and it works great.
Hey all, for a while i was considering purchasing a griffin powermate, or something simmilar, to control volume in my car pc. however, i recently came across a much simpler solution. i found a little application called volumouse. it lets you control your pc volume using the scroll wheel on ur mouse. i installed this, and then butchered a cheap usb mouse, just keeping the scroll wheel. after you've doen this you can mount the scroll wheel wherever you want! i just have it in the center console for now, but it wouldnt be hard to mount in behind the dash and attach to a stock looking knob. and presto, you have a proper volume knob, mounted wherever you want! the software is a free download from CNET (www.download.com). enjoy!
ive used volmouse for years on my desktops. it doesnt work quite as well in vista, but it is still works most of the time. (vista handles application sounds all seperate, sometimes volmouse doesnt know you want the sound changed)