How much do you already know about computers or programming? The industry grade stuff is really expensive, but in schools, if your using anything fancy typically the program will be made available to you in class or in the computer labs. If you don't know any programming yet, hold off on spending large amounts on a program for this kind of thing. Learn more about computers, how they work, how they're programmed, and then look into graphics engineering. I honestly think everyone should best start with the fundamentals
That said:
If you want a free option that's very simple you can do very simple and basic graphics programming on any computer with a simple C/C++ compiler and the OpenGL library, both of which can be downloaded for free online from numerous places (Microsoft has a free version of Visual Studios and the Visual Studios SDK). There are a lot of tutorial websites that will help teach you how to use it and how to program in OpenGL and C/C++. If you're using a Mac, it comes with a built in compiler, though it can be a little annoying to use at times because you must access it through the terminal (You can do the same on a
PC through the command prompt IF you have the libraries you need) but the option is free and doesn't require you to download a program. Some Macs come with OpenGL I think.
For general programming (no necessarily graphics) you could download Eclipse, and play around with Java. It's a very easy language to figure out and doesn't have some of the complexities or minor annoyance of C programming.