I have been trying to design a case that fits into a double din space (based off of dimensions that I have pulled from sources online) and this is what I have come up with so far. Still lots of work to be done, but I thought I would share this, and get opinions.
Sorry for the poor quality, SketchUp apparently doesn't export too kindly.
Green = Hard Drive
Red = MoBo
You won't be able to fit a mini-itx board in a double din space. Also, if you somehow do get it to fit, when you decide to install a real os like LinuxICE, it'll be a pain ripping it out. That same difficulty will apply when your windows blows up, your harddrive crashes, and/or you just want to upgrade or install some software.
i believe that tripzero has a impala as well, so take his advice :)
for the dash install, i tried it in my car(if your curious, my radio has about 12-13" of depth), and i had so much trouble just getting everything to fit, and wired that i quickly scrapped it for a under seat install-- i would highly recommend to locate the pc elsewhere for heat, serviceability, and ease of access
there isnt that much space in the dash of an impala i can tell you that for fact. i have an 04 and thought about putting mine in there. it just wont fit. as far as the trunk thats about the only place in our car that makes sense. the passenger seat has a spring and track not to mention a hump that keeps that area from being useful. the driver seat isnt even an option lol. if you have a center console that might maybe be a shot. if you have the the bench seat then the hump in the floor will keep you from putting it in that spot. so by deduction that really on leaves the trunk as the viable pc spot. o yeah i forgot the glove compartment...well just look at it and how it goes in and out and youll know thats a no go.
i just put the lilliput in the dash and the pc in the trunk. for cases im "borrowing" a members psp/poker chip case idea. just looks interesting and helps for portability while still being fairly small in size.
ive run both with a sound card and without and i can tell you that the impala is not a very acoustically friendly vehicle so if you can save some money here you should