Download this free graphing calculator for your PC
Microsoft Mathematics 4.0 provides step-by-step instructions and visual ways to explain complex problems for a better understanding of fundamental concepts in pre-algebra, algebra, trigonometry, physics, chemistry, and calculus.

From basic math to precalculus, Microsoft Mathematics 4.0 can help you visualize and see mathematical concepts as you’ve never seen them before. This free downloadable tool includes step-by-step instructions and explains fundamental concepts. The wide range of tools to help students with complex mathematics includes a full-featured graphing calculator that’s designed to work just like a hand-held calculator and ink handwriting support to recognize hand-written problems.

Other Free tools for the classroom:
http://www.microsoft.com/education/teachers/guides/freetools.aspx