I too am a newbie to both the PDA and Axim world; however, I will do my best to answer your questions.
1) Most software downloads will list the Intel XScale as one of the accepted processors.
2) Most software made for PPC2002 will run on your MS2003. If the program was written in eVB you may be asked to install the eVB runtime files. Available
here.
3) The "other recourses" >> "downloads" have a few links to different productivity utilities, including a calc.