My two bits....
I have heard very good things about Ubuntu, MEPIS, and SUSE. I recommend any of the three. However, the more important question you may want to ask is "What window manager should I choose?"
Since you are new to Linux, here is my advice:
1. To truly learn it, you need to use it. Unless you are very disciplined, I don't recommend a dual boot if your goal is to learn the operating system and window manager. Most new users need to get rid of the Windows crutch and force themselves to use the OpenOffice apps, file managers, Gnucash, and other Linux apps. With a dual boot, you'll likely boot into it a few times, say "Cool, I did it! Time to update my resume." and then you'll never use it again. Also, while you're forcing yourself to use it, make a commitment to make all the hardware function, you will learn exponentially. I recommend a 90 day commitment to the operating system for your work PC (you'll want to keep MS Windows for home use if you are a gamer or a videophile), after that, if you don't like it, go back to MS Windows.
2. If you are comfortable with MS Windows, I recommend KDE as your default window manager. Whole dissertations have been written on KDE vs. Gnome, but when it comes down to it, KDE is easier for the average user famililar with MS Windows. I personally prefer Gnome, but that may be because KDE didn't even exist when I started playing with Linux.
3. Beyond that, any desktop-centric distro is good. What really seems to be differentiating them nowadays are the install programs and the window manager configurations. Of course, what works out of the box is a big factor as well. Package management has become pretty solid across the board, and nearly all of them come with OpenOffice and a graphical web browser.
In a nutshell, for a new user, I recommend any of the following:
MEPIS (a live CD with an option to install, good to play with at first, kind of the 'try before you buy' mentality).
http://www.mepis.org
Ubuntu (haven't used it, but have heard nothing but good things).
http://www.ubuntu.com
SUSE (easy to install, looks pretty, and has a solid rep for being stable). Note: I used to hate SuSE back in the day because I associated it with Carolyn Meinel, but I have learned to look past this stigma on SuSE.
http://www.opensuse.org
Fedora (Redhat's been around forever, easy install, good market saturation, etc.).
http://fedora.redhat.com
In conclusion, a dual boot in our modern days of multi-PC households, VMWare, massive RAM, giant hard drives, super processors, and video cards made to track a bullet in real time doesn't make a whole lot of sense in my world unless you need all your system resources for compiling and other resource intensive tasks when your using linux.
Again, this is just a matter of personal taste. I just think you'll use the OS more if you have quick and easy access to VMWare on your desktop then if you have to shut down and restart every time you think about using it. Actually, in all likelyhood, you'll probably use it only a few times if you choose to go the dual-boot route.
Of course, take my opinion with a grain of salt. I was a devoted Redhat/Fedora user till just recently, and am now getting back to playing around with the millions of new distros that have popped up in the last couple of years. I continue to be flabergasted by the improvements in graphics, applications, and stability.
Cheers,
djc