Rules Compendium pg 7
"Restricted activity: A few situations make you unable to take a full round's worth of actions. In such cases, you're allowed to take only a single standard action or a single move action, along with allowed swift, immediate, and free actions. You can't take a full-round action and finish that action, but you can start or complete a full-round action by using a standard action."
Also note pg 27
"Charge
Restricted activity: If you're unable to take a full round's worth of actions on your turn, such as during a surprise round, you can charge as a stadnard action. In this case, you can move up to your speed rather than up to double your speed. All other rules for charging apply."
Which allows zombies to charge.