Dual monitor support is a feature of X, and not necessarily the distro of *nix. There are tons of HOWTO's and FAQ's about dual monitor support and Xorg, for example one from the Gentoo Wiki is
here. There are many more on Google, just search for "xorg dual monitors".
If you're new to *nix, then I'd probably suggest
Ubuntu as a distro to start out with. It's supposed to be real easy to configure and use, and the apt package system is known for being easy too. Then you can apply any changes to your X config file for dual monitor support.
-Mark