Apple or PC?

I am in the market for a notebook computer to use for University. I will be using it for research, writing papers (word/excel), sometimes taking notes in class, music, some photo editing, the odd DVD on trips, and internet surfing. It must be around a 12" and under 5 pounds with good battery life. I have been reading and it's my understanding mac OS X is a more stable operating system and that it is more secure from spy-ware and virusus. They also have 128Bit enscryption I hear as well. The powerbook 12" model looks perfect for my needs but my buddy who is a computer guru says macs are only good for photo editing and I will run into compatibility issues with the mac becasue they dont use a system registry or something like that. What should I do?