This is an age-old question... which distro is best. The answer is always, "It depends".
For someone new to Linux, who just wants to see what it's all about and not screw up their current computer configuration, I'd recommend one of the live CD distributions.
Of the live CD's (they're called live CD's because the operating system runs from the CD, usually loaded into RAM, and not from the hard drive) the one I'd recommend to start with is DSL DSL webpage. It's a very small download (less than 60meg).
Download the ISO, burn it to a CD, boot from the CD. You're up and running under Linux (DSL is a Debian type configuration). Once you get your feet wet you can decide which of the Big Gun distros you really want and need.
Just my opinion. Good luck.