Hi, welcome to the site!
If you want to use your PDA with EMIS - they have a couple of solutions you should look at:
PalmGP -
http://www.emis-online.com/palmgp.asp
Palm Mentor -
http://www.emis-online.com/palmmentor.asp
It looks from their website like they only support Palm OS PDAs:
"PalmGP currently operates on Palm M130, Palm M515, Palm Tungsten T and Tungsten E devices."
I would suspect that it will also work on new Palm devices but if you are interested in this product I would ring up EMIS and discuss it with them.
Any of the Palm devices will be able to store your protocols and reference mater and you'll also be able to make notes in meetings, lectures and home visits on most device.
The Oxford Handbooks are now available and will work on most Palm OS devices. If you are planning on installing several of them, make sure you add up how much memory you need and buy a PDA with enough on-board memory to store them all. You can also buy extra memory later through a larger SD card.
As for the BNF, it's currently only available from a company called MedHand -
www.medhand.com. They have a product called Dr Companion which includes lots of UK software such as the oxford textbooks and the BNF. The main drawback with Dr Companion is the huge price tag - somewhere in the region of 350 pounds. They were saying that they were going to release the BNF as a seperate product so it's probably worth getting in contact with them and seeing if you can get the BNF at a cheaper price as a stand alone product.
Hope that helps a bit, let me know if you have any more questions.
BTW - are you just after a stand alone PDA or do you want a PDA-phone?