1. ease of use
2. very popular
3. good looking interface (even classic style)
3. lots of documentation
4. lots of tech support when you need it
5. its been around for a long time so its had years of expierince to get good
6. very very supported by software and hardware
7. not much knowlege of computers is needed to use
8...more to come cant think right now, im tired
2. very expandable (open source)
3. nice interface (if tweaked through the options to look nice, stock interface is ugly)
4. defaults with 4 working desktops that can easily be switched through
5. comes with many programs that do things you would have to pay for on windows (office style programs)
6. loaded with server tools and applications to run right out of the box. (better than that IIS crap)
7. comes with tools for developmental enviroments (programming and such)
8. its free and easy to install
9. dont need to be an administrator to be able to use the OS's good features that are common in use (downloading, and such)
10. lots of help for it, very large user group.
11. lots of tools out there to port windows programs
12. built in pop-up blocker with the os
i like windows more. but i think Linux has more plus's but is more for that advanced user, thus i perfer windows, though i have my own linux box from which i like to do work on every now and then.
You should compare Windows and Linux or Mac and Linux because it's possible to run them on the exact same hardware.
Without an emulator of some kind, Macs will not run Windows and PCs will not run Mac OS.
It could be interesting to compare "innovations" in Windows with innovations (no quotes here) on Mac. Macs have been talking to you for a long time, and now you can talk to them without extra software. Trash can...recycle bin. Finder Menu Bar...Explorer start menu... just to get you started. ;-)
CP/M vs. RedHat is my choice. Just kidding, I suggest comparing XP and whichever flavor of Linux it is that looks almost exactly the same GUI-wise (is that Knoppix...?). I think this would be a good comparison because looks is no longer an issue.
Personally, I've never used Linux for more than 2 minutes at one time (I had no clue what I was doing... it was so different from Windows) so maybe you shouldn't listen to me, but XP and linux are basically polar opposites, so try comparing them. If you had to debate it, it would become almost as heated as a debate on politics or religion, I believe:).