I don't know anything about the NM10 video chipset. You say you want video. Does the NM10 do hardware-accelerated decoding of h.264? I know the ION platform does, but costs more. Then again, h.264 may not be important to you.
For the hard drive, I'd stick with the laptop hard drive. Desktop hard drives won't fit in many of the smaller car PC cases, which brings me to:
You don't mention a case to put all this in. Are you building your own enclosure?
Memory: 1GB is fine.