Concerning the calculator, you might look into Formulae 1. It's a Java based program that seems very promising. It offers step-by-step solutions and symbolic manipulation. My Axim is currently in the hands of UPS so I don't know how well the program works, but the author assures me that it is Axim compatible. I am not sure if the Jeode software comes with the Axim or if it is a seperate purchase, but it is required for this program.
I have a TI-92 that I am wanting to replace. The TI calculators are good, but I have had to replace them too often. (Worn out buttons, etc..) The functionality and programability of the Axim is very alluring. And at nearly 2/3 the price of the Axim, it's hard to beat. There are a number of calculators and equation solver programs available, and surely more to come. So I took the plunge. Also, there are some very interesting electric circuit simulatiors soon to be released for the Pocket PC.
I am currently taking my second course in Differential Equasions, and my instructors since Cal III havn't cared what we bring to class. The tests have been designed in such a way that a calculator doesn't help too much. ("Show your work" kina' thing) But it is nice to check your answer.
Let me know if you fin anything interesting.
http://www.poliplus.com/