The Macs are basically PCs with a different operating system on them.
When it comes to photography, they can both run the same software - most photo-related programs are made for both platforms.
However, if you want to use your computer for a wide variety of things - say games - the MACs are the pits, since most games are made for Windows.
Windows XP is fairly stable now and runs fast. If you're hung up on the GUI, you can always install a shell program like windows blinds and stardock and knock yourself out with doo-dads.
Apple is a brand name, using common generic components wrapped in a unique - and for some - pleasing design, paired with an operating system that is well suited for beginners, since it's so user friendly.
But that comes with a surcharge. Whether it's worth it, is an individual preference of course.
I choose to use a Windows PC because of the much larger selection of software for it and because it is - by far - the most common operating system in the world. Sure, I might find MAC OS more intuitive, but having been on the Windows platform since Windows was introduced, it's second nature.
However, VISTA is an unmitigated disaster..lol.