I put a snow leopard disk into a old slot loading 600 mhz IMAC running 10.4.11 with the intention of upgrading it. Now I'm getting a gray screen with flashing question mark. I didn't do anything but insert the disc. I can't get the disk to eject. The question mark means the computer can't find anything to boot up from. What should I do next?

Your computer does not meet the minimum specs for snow leopard.
The install disk is a DVD also not a CD like 10.5 had.

Try restarting and holding down the command and C keys at startup. This should eject the disk. If that doesn't work, restart with the mouse button held down. This is also to eject the CD. If it doesn't boot correctly after the CD is out, restart holding command, option, O and F. This should bring up an open firmware command prompt screen. Type in "reset-all", without the quotation marks, and press enter. This will restore the PRAM and NVRAM to factory defaults and should allow normal booting. It may take a bit longer to boot the first time after you do this.