Replacing a G5 ("Table Lamp") iMac's hard drive.
1.) Tear out all the screws on the bottom; both the RAM and non-RAM.
2.) Peel off the top case. Ignore the ripping metalized plastic, it's unavoidable.
3.) Pull up on the black tab holding the hard drive in.
Granted, this didn't help our particular iMac, which had a bad SATA port on the motherboard. But it might help somebody, somewhere!