Speaking as someone who's been mucking about with Linux since the initial builds (back when Slackware WAS the only distro!), I would also join the folks recommending Ubuntu as a distro for the new Linux user. (I've also found that, driver-wise, Ubuntu seems to be a bit better-behaved than some other distros.)

If you go the Ubuntu route, you *will* want to get a tool called Automatix (http://www.getautomatix.com) which has an installer for Thunderbird, VNC, etc. as well as codecs for video and audio that can't be shipped with Ubuntu proper (due to DMCA restrictions, some software being freeware but not open software (the big ones here being Google Earth and Skype), etc.

OpenSuSE is also not bad at all--I used to be a diehard SuSE fan until the "commercial" fork of SuSE got so huge the distribution covered *multiple* DVDs OpenSuSE is close to how SuSE was before the commercial fork got bloated to heck, and is a good compromise between usability and power. (Of note, SuSE is *still* pretty much the big distro for commercial use in Europe, much as RedHat/Fedora Core has tended to be the big commercial distro here--though a *lot* of that thunder is now being stolen by Debian-based Linuxes like Debian itself, Ubuntu, Mephis, etc.)

BSD...most of the people I know using BSD are using it for dedicated servers, and servers and firewalls is really what xBSD-based OS's are best for; for workstations, you'll seriously be better off with a user-friendly version of Linux like Ubuntu or OpenSuSE. As others have noted, programs are not necessarily cross-compatible and there is actually more development support nowadays for Linux in general. (The ONE big exception to this is MacOS X, which is actually a BSD derivative with a non-open window manager; yes, you can compile and run ports of BSD-runnable applications on MacOS X. However, 99 44/100% of the folks using Macs aren't running it because it's the world's prettiest flavour of Unix out there! )

Now, the next question--once you pick a flavour of Linux, what window manager do you want? Ubuntu ships with Gnome, many other commercial distros ship with KDE. You can install the toolkits to use KDE stuff on Gnome and vice versa, though (and Ubuntu IS quite intelligent about this); there's also a KDE version of Ubuntu called Kubuntu you can use if you want to standardise on one window manager. (There *is* more support for KDE out there than there is for Gnome because most commercial distros (outside of Debian-based ones) use KDE, so that may influence your decision.)

As others have noted, you can actually make Linux *very* pretty (as pretty as MacOS X, in fact)--this is done by the window manager add-ons Compiz and Beryl (Beryl is the newer version of Compiz) that allow you to do Mass Prettiness to your display that tend to make Windows Vista users green with envy . You don't *have* to do this, but you can if you want. One of the beautiful things about Linux is that you can pretty much choose what you want. Gnome and KDE both are pretty mature, slick window managers/GUIs.

One thing I WOULD recommend, especially if you are brand new to this--get the live-CDs for Ubuntu, Kubuntu, Fedora Core, and OpenSuSE and run them on the target PC to see which works best and which you like the appearance of the best. (Some distros have their own quirks, and you might find that things run better under one distro rather than another.)