Dude. NEVER tell someone you have a crush on them. It just never turns out the way you want it to. I had a crush on this girl and I knew the only way I'd have a chance at her was by first becoming friends and so I did. We talked in class, over the phone, hung out, and then I asked her out. She's been my gf for the past 9 months now. Be casual. Be cool. DON'T be socially awkward (it's hard not to be when you're with someone you like). Don't jump out and scare the crap outta them. That's almost for certain what'll happen. They'll be surprised, flattered, maybe even a bit weirded out. In your case, this guy turns out to be straight, you might even get laughed at, made fun of, and will be talked about among everyone. I don't want to scare you or anything but right out telling someone you have a crush on them IS NOT the way to approach someone who you like. Talk to him, introduce yourself, and become friends.
This, my good friend, is what the "friend-zone" is for. It is a safety net used in any purpose situation. They allow you to get to know eachother a lot better and will avoid any awkward levels of mutual understandings. If you get to know this guy and he's what you wanted, you're in the clear and it's smooth sailing from there. However, do not remain in the friend zone for too long. A month at most before asking them out...otherwise, it'd be like asking your childhood friend of 10 years out on a date out of the blue.