is there any essential software that I'd really need that only goes one OS or another?
Epocrates is free for the palm and is essential. Helps you quickly look up dosages, mechanisms, side effects, or if you just wanna quickly see what the generic/trade name of a drug is (much fast than say accessing the pocket pharmacopia)
I have a dell axim xxx model, who cares. I haven't used it since my medicine rotation, just use my pharmacopia now. As teched out as I like to be it's amazing how I've regressed. Might use it more in surgery, I don't know. Don't get one unless you really feel you need it.
Have a pocket pc myself. There were times i'd have liked to have a palm OS, since my classmates were busy beaming their free programs to one another. Free programs for pocket pc are a bit harder to find. Used my PDA mostly for the calendar (keeping track of where i was supposed to be for conferences, clinic, etc) and Epocrates in 3rd yr. Now, as a 4th yr, i've also "regressed" to using my tarascon and other paperback references. I've used my PDA so little this year that my main battery ran out, and i need to totally reload everything back onto my PDA after i recharge it.