Perhaps you could clarify this?
When you say it was meant to, was it part of a promotional offer with say ATi, because I know they were giving out free coupons for HL2 on its release.
You are not legally allowed to download the game if you don't own the original, without some proof of purchase. You also need a CD key for said above game, and again, if you don't have one, you won't be able to use it legally. I'm not sure if it will work online at all, if a duplicate CD key is entered.