Trouble copying games.

[The Disco Kid]

Im new to the cd copying game, only having my writer for about a week. Im trying to copy a game cd using nero 5.5 but i dont want to finalize the cd so i can add some extra files later. Ive tried a few things like an iso cd and a udf cd but when they have burned and i try and run the disk im told that it's not a valid aplication. But if i just copy the cd (finalizing it) it works fine. Any help would be realy apreciated! Thanks alot.