OSX Snow Leopard USB Booting

Hey guys, I've been considering upgrading to snow leopard since I can't download portal 2 (says a lot, doesn't it?)

I have a USB over 8 GB's and I can easily get snow leopard. Partitioning the USB isn't a problem either, but how would I boot the new OS onto my iMac through my USB? I know there is a whole thing with pressing C at bootup, But isn't that only with my DVD drive?

 

Thanks,

Sai

Have you tried pressing option when the book screen is showing?

Yes, that worked for me. Now I can finally move on to newer revisions of Mac OSX. Thanks!