Carol, in case you didn't realize it, the problem might not be on your end. It could be the particular form that's causing the problem. Not all forms are created as "interactive." If the creator did not create an "interactive" form, I don't believe there's anything you (OR a PC user) can do except pull out the old typewriter or pen.
If you'd like to test a form that's definitely interactive, try downloading this one:
http://www.utc.edu/Administration/Admissions/secure/UTCApplication.pdf
I've just tried this particular one and had no difficulty using Adobe Reader 8. You shouldn't need any "tool," rather simply click on any of the interactive fields and start typing.
Incidentally, interactive PDFs also work with Preview, the program which comes with OSX, so you might wish to try that as well. It also worked fine for me on this particular form.
If the form turns out not to be the problem, be sure to post back as I'm sure someone can help figure this out. You definitely should be able to fill out a PDF form, so long as it was created as interactive.
iBook G4 1.42GHz PPC, 14" Mac OS X (10.4.8) also iBook G3 600MHz/ MacOS 10.1.5