Macs run Windows pretty much out of the box, run Mac OS X (a UNIX based operating system, basically Windows only prettier and statistically more stable.
Operating systems wise, Windows has more apps, although most are, well, rubbish ("Clock"... wow). Macs have less apps, only generally they're a little better, quality-wise (Microsoft Office has been shown to perform better on the Mac, media programs (movie players, music players and creative things) are generally more accessible and more powerful for the money (Shake, Final Cut, Keynote, Pages etc).
Personally, having worked with multiple systems
(in order, BASIC, DOS, RISC OS 3.11, RISC OS 3.7, Windows 3.1, Mac OS 7.5.1, Windows '95, Windows '98, Mac OS 8, Mac OS 8.5, Windows 2000, Mac OS 9, RISC OS 4, Windows XP, Mac OS X, BeOS 5, IRIX, AtheOS, ReactOS, Sun Solaris (10 I think, the most recent one), Sun Looking Glass (3D operating system, got a preview
), Linux (most of them
), RISC OS 5, Windows Vista (shhhhh...), QNX (Momentix I think) and even Rhapsody(!)
...and although I personally prefer RISC OS and BeOS in terms of fundamental design, I must admit that Mac OS X is by far the best option considering ease of use, aesthetics, stability, software available and so on.
Hardware-wise, many cheaper PC manufacturers actually use the screens and components that Apple chucks out, so yeah...
I'd go Mac without hesitation.
[EDIT] If you have to use Windows, think twice about Dell. For VERY basic use they're great, but if you want to do anything vaguely demanding (such as playing music

) they tend to fall apart pretty quickly.
You get what you pay for.
Rich::