no disk drives do not go into PCI slots. they are connected to the MOBO through cables. HDD(hard drives) can either beconnected by a IDE cord or for better performance by a SATA cord. CD/DVD drives are usally by IDE cords. there are some that use SATA cords but they are expensive.
i good MOBO that i like is this one:
it's not SLI enabled though.
And about this:
"SPEED INTERFACE BUS SPEED PRICE
650 / 3.4Ghz Socket 775 800MHz $429.99
560 / 3.60GHz Socket 775 800MHz $425.99 "
the 650 is a newer model then the 560 thats y it costs more. i would go with the first one.
this may sound mean but i really think you should find a cheap $50 computer at a garage sale and take it apart to see how everything is connected before you start to build a computer. i think you need to do a lot more research into how computers are built before you you attemped to build one. try and find some old threads about building computers here and read them then anything you don't understand come back here and ask about.