Hi senseiblackbelt, welcome to the site!
If you want something similar to a Sony you'll be looking for a Palm OS PDA. Something like a TX might suit as it is reasonably priced and has good specs and will run most medical applications.
Do you need to have phone functions? If so you might want to have a look at the Treo 650 which is a very nice Palm powered phone.
Memory level depends on how many applications you want or need. Even with no medical apps a PDA can be very useful in a medical environment but you'll probably be wanted a couple of apps. 5minute clinical consult, Harrison's and epocrates are all very popular programs you should probably take a look at. Skyscape do Harrisons and 5mcc as well as a range of other apps - you can download free trials from
www.skyscape.com, epocrates is from
www.epocrates.com. Check out the memory requirements of any programs you are going to get and add them up (plus a bit more) to work out how much memory you'll need. If you get something like a TX with 128MB you probably won't need an extra memory card to start with but you can always get another one at a later date.
If you want to keep a patient database, I'd recommend HanDBase from DDH software -
www.ddhsoftware.com. It's fairly easy to set up new databases and it's pretty powerful. You can also download as a free trial.
Let me know if you want any more info - if you have any specific questions, start a new thread in the Palm Forum -
http://www.doctorsgadgets.com/forum/medical-palm-forum/ if it's about Palm OS machines or PDA Software forum if it's about software -
http://www.doctorsgadgets.com/forum/...-pda-software/.
Cheers,
Chris