Sounds like a pretty decent idea. Why not use the FM tuner, remote, vol control and stuff from the mobo? Much simpler than just adding in more stuff, since you already have it. It's not all that much effort to hook it all up, and once it's hooked up you don't need to do it again.
You really don't need a CDRW in your car, and DVDs are pretty cheap, you might want to do that instead.
You can use your hard drive no matter what, just set the BIOS to the max that it will happily support, and install Windows XP (which doesn't even use the BIOS for hard drive parameters) and you're good to go. You don't even need to use their boot loader program, but you can if you want to.
The PSU is fine, and not all that expensive either. Do you really need a small PSU though? You'll probably have room for a fullsize if you're planning on having expansion cards.
What's your budget on this anyway?