[quote name='pun123']Just got mine today went to install and steam said it was a duplicate CD key, so I emailed newegg and lets see what they say, sucks.[/QUOTE]
If Newegg doesn't help you just send a support ticket to Steam. They will ask you to send in a photograph of the key showing that you own it. They should be able to take care of it for you. Plus, I think the person who used the key gets their account suspended for theft. At least that's what I've heard. Yay.
Either way, Steam should be able to activate the game for you since you can prove you own it.