Being intelligent animals, rabbits can be litter-trained! By nature, rabbits choose one or a few places (usually corners) to deposit their urine and most of their pills (poop). Urine-training involves a little more than putting a litter-box and litter (Breeder Celect's cat litter is a great option).
When you first start, you may need to limit the circumference where your rabbit can roam freely until you're sure it's getting the hang of using the litter box. The trick is to start small. If you have a playpen, you may place the litter box in a corner where you tend to see more pills. Stay away from litter made from softwoods like pine or cedar shavings or chips as these products are thought to cause liver damage in rabbits.
As with all pets, a little patience goes a long way. In your rabbit's own time, it should be litter-trained soon! Find out more by researching on the internet. Here's a good page to start you off.