You will push against your opponent, then you will go flying in opposite directions from him (unless he is grabbing you, of course). You wouldn't need a base.
But you do have mass. And since you have no weight, you could do great flying kicks if you have a base to start from (like a wall).
Except for when you are up against the space station walls.
Remember that a lot of locks/breaks depends on the weight of the opponent to work. They still might work if pulled off fast enough, though. Then you would be using the inertia of the opponent instead of his weight.
True. Remember, kids: In space, no one can hear you tap.