I think you're going to be ahead of the curve, art and level-design wise. You won't get a chance to do any heavy work in 3-D until year 2, probably. But! You WILL be in very high demand then. Not enough good artists in this major!
Though you have to understand that the major is %75 computer science and %25 art and design. What will really prepare you to enter into the major is a basic understanding of programming.
The programming track has two possible starting routes. If you know nothing or very little about programming, you take courses CMPS 5J and 11. If you have at least a basic understanding of any kind of programming language, you (should) take CMPS 12A. 12A is the same content as 5J and 11 combined into one quarter. So you can get yourself a bit ahead, especially because 12A is offered in Fall, but 5J isn't offered until Winter.
Here's the curriculum chart. http://ua.soe.ucsc.edu/sites/default...GD_09-10_0.pdf
If you'd like more in-depth info on what to do to prepare for 12A, I can give you some pointers.