I am trying to download leopard to my G5 but when it restarts the screen goes gray with the spining wheel someone help me.

Hmmm... try leaving it for a bit, and if it doesn't do anything in an hour, i would try rebooting. Other than that, I don't know.

I tryed that and it goes to sleep mode

You're trying to download leopard? Well there's your problem. While it's possible to download it (as illegal as it may be), getting the computer to run a massive update like that is kinda hard since the update has to be run from startup. How is it going to access the file if the computer isn't started up, you know? The reason it comes on a DVD is because it's a boot-able disc as well. Just go out and buy it!