If one of your brake light bulbs is out or the fuse to them is blown, the vehicle will not shift out of park when the button on the gear selector is depressed. This is a safety feature installed by toyota.
Until either the fuse is replaced or the bulb is replaced (which ever one is the problem), you'll have to get a screwdriver, pry open the clip next to the gear selector and manually unlock the transmission. (I've had to do this before on a friend's 4Runner before.)
Once the brake light issue is fixed, you will be able to shift the gear selector out of park like normal.
A friend of mine had this happen on his '98. Come to find out, it was faulty wiring on the trailer that caused his brake lights to short out, thus blowing the fuse. This in turn would not let him shift out of park.
Talk about a strict safety feature...