yeah i put a cd rom drive in my car when i was poor and couldn't afford a cd player deck and had a spare cd rom drive. they're pretty good - mine didn't even skip much! i used the 12V and 5V regulators bolted back to back to a heatsink. i opened up the CD drive and my tape deck which had a cd input on the back and tapped into the phones out on CD and CD in on tape deck, ran the wires around the back and put the cases back on. the only thing to remember is that the CD input jack on the tape deck has a switch to switch to CD, this needs to be shorted, or put a switch in a panel in your car (this is what i did) incase you want to use the tape and radio as well. Good luck mate.
CD rom drives are great coz they'll read CD-RW discs as well. unfortunately, its really hard to make it read MP3s. probly cheeper and easier to buy one.
Good luck mate.
Josh.