alright, so i did this.. and it will work for you too, this is not illegal
1.) when the free weekend starts again, right click on the game.
2.) look for a tab that says "cd key"
3.) click it, copy it in notepad.
4.) torrent the .iso (ONLY IF YOU HAVE "MISPLACED" CD'S
)
5.) install game put cd key in.
6.) thank steam for the free unreal tournament 3