First you need to purchase one of these adaptors for a dollar, this way you don't need to cut any wires on your atx power supply. You need to cut the yellow wire and the black wire next to it on the adaptor, these are your 12v and 0v rails. Connect the power in and remote turn on of your M2 to the yellow and the ground of your M2 to the black cable.
Once you have done this and made sure you have properly insulated the joints you made with insulating tape or something similar to ensure you don't shock yourself/fry your carputer you can connect this adaptor to a spare molex socket in your desktop PC.
Switch on your desktop PC and your carputer will come to life 5 seconds later.
Now installing sata drivers may well be your next hurdle although I have found some combinations of certain motherboards and certains versions of XP don't need any drivers from a floppy or slipstreamed cd/dvd. I'll leave the sata installation part to somebody else to help you with as slipstreaming takes some time and patience, usb floppy drives are quite a cheap and easy solution though.
I'll post pics tomorrow if you like?