well, if you want more information on how this site work, just check the : F.A.Q you will learn a lot about how it work :D

But for creating giveaway of a game, it is not an obligation to own the game in its steam library, its just that having this game will make you less suspicious of creating a fake giveaway BUT you need to Have the game to give (by that i mean you must have a valid steam key to give, or buy it on steam to offer to the winner of the giveaway you created)

If by what you said you mean that you don't have either a key or gift to give of GTA IV, and don't plan to buy to offer to the winner, then you better closed this giveaway (normally there is an option in the left column of this page for that) That way people won't be mislead and waste point entering the giveaway for nothing, and you won't get punished for creating fake giveaway, and won't leave a bad impression on our community :D