Does GNU/Linux run on Apple hardware?

I love Apple's hardware, but don't really like their software much.
Am looking to purchase an Apple workstation, but would like to run some 
GNU/Linux distribution on it.

Questions;
1. Is there any GNU/Linux distribution which runs on Apple hardware?
2. Is it legal to run some other OS on Apple hardware?
3. If another OS is run on Apple hardware, does it void warranties?

Please avoid sending in responses stating that Apple Mac OS X is better 
than GNU/Linux in some way. That might be true, but personally, I would 
prefer GNU/Linux.

Thanks,

~Mayuresh

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