Hi Mikey, it looks like you have an Alpine deck "going into" a computer motherboard. What were you planning on using as the interface for that? I've read that M-Bus and Ai-Net are Alpine's aux input methods, but it seems data for bi-directional control is a vauge holy grail. How were you planning for that to work? RCA input adaptor then use the touch screen to control the media player? I'm a newbie too so just wondering how you were planning to do that part.
I second Peoples concern over the use of an inverter if you have a dc-dc power supply. Is that a 3.5" or 2.5" HD you are using? How about the optical drive? Is it a slimline or standard type? I'd recommend on going with a low power 2.5" HD and slimline optical drive if you haven't already purchased the equipment. That's why you went with the EPIA M series to begin with, right? If you do have a dc-dc power supply then you could get a Carnetix P1260 regulator/shutdown controller and be fine with all low power devices. It might not be enough to handle a 3.5" HD and a standard PC optical drive though.
I third People's concern. But if you are going to use an inverter (knowing full well the risks and inefficiency since you did your research by searching "inverter".....right?), I would go with a full sized 3.5" drive. the reason is that while laptop drives are much smaller, they are also much more expensive and have a lot less space on them. For the price of sometimes as little as 1/4 of your laptop HDD you can get the same size HDD in 3.5". on the other hand, slimline DVD drives are dirt cheap and very easy to manage, with no noticable performance loss (IMHO).
Either way, as Jeremyp pointed out, get your power situation squared first, then get the components that fit that power scheme.