Using this Trainer:

Launch the trainer first, then launch the Game and then Press F1 at the Main Menu.

Listen for "Activated".

Press desired option key

Options in Promo:

Numpad 3: Mega Damage

Options:

Numpad 1: Mega Health

Numpad 2: Mega Money

Numpad 3: Mega Damage

Notes:

Numpad 1: Mega Health - toggle on and your units have unlimited health

Numpad 2: Mega Money - toggle on and you have plenty of money

Numpad 3: Mega Damage - toggle on and most low level zombies are killed quickly.  May not work against all zombies.