I've put new (extra) RAM and a new HD in my PowerBook G4 - easy as pie just so you're careful and know what you're looking for. Yes, you can. Just so it's not a laptop as I'm not sure how you'd do that there. My point is you CAN upgrade critical pieces like RAM, video cards, and hard drives if you know what you're doing and use the right parts. My only complaint about Apple (in general) is the price of their RAM - they use really great stuff and you know it'll work but I personally would purchase RAM from Kingston or another site like that and install it myself. Anything that uses any PC-only extension cannot even run on a Mac, so you're very correct. The viruses (that I know of) for Macs are very hard to get because no one wants to mess with designing viruses that hack into the Unix-like shell. From what I've been told by programmers it's not a lot of fun to try and write exploits for that system but I know it's been done.