The main advantage of VMWare is that you don't need to dual boot. You can remain in the ``host'' operating system that you feel comfortable with (for most people, it is Windows). You can use the ``guest'' OS only when you need to. You also have access to both OSes at the same time. Copying and pasting across the OSes can be tricky, but the two OSes can share the same file system(s), which makes it easy to transfer files from one OS to another.
Another cool thing about VMWare is that the ``guest OS'' can be completely shielded. The so called file system for the guest OS can be just a huge file in the ``host OS''. This means the ``guest OS'' can never mess up the ``host OS''.
VMWare also allows the ``guest OS'' share the same network connection to the internet with the ``host OS''. This is very cool because now your ``guest OS'' can access the internet resources.
I only have experience using Linux as my ``host OS'' and Windows 98 as my ``guest OS''. If you want to set up VMWare in the opposite direction, I can only give you a few pointers.