Quadra 630, Performa 630/6200/6300 Series, LC 630, Power Mac 6200 and 6300 Series
Logic Board
The logic board in this model is extremely easy to remove. Press the tabs on the back of the machine and tilt the back plastic panel down and off. Remove the two screws in the metal area that was behind the plastic panel. You can use the "handle" built into the metal area to pull the logic board out. It's in there pretty well, it will take a firm pull.
Hard Drive
Find the two "latches" on the underside of the front panel of the machine. Stick a flat blade screwdriver to the latch and pry the latch up. Do this with both sides. Tilt the front panel up. Be careful, it's pretty easy to break something in there. There is a metal piece that prevents the drives from being removed, you'll need to remove it by taking out the one screw that holds it in. Disconnect the cables from the hard drive. Next, pull the hard drive out by pushing up on the tab beneath the hard drive. It's easier to use a screwdriver.
CD-ROM Drive
Follow the same steps as the hard drive, but remove the CD-ROM drive instead, by pushing the tab underneath it up. Once again, it's easier to use a screwdriver.
Floppy Drive
Follow the steps for the hard drive, but instead of removing the hard drive remove the floppy drive by pulling up the floppy drive and pulling out. Don't pull out too far, you still need to disconnect the cable from the back of the floppy drive. Once you've disconnected it, you can pull it out all of the way.
Information provided by Doug Brown.