You mean the Apple operating system?
Simple answer=no...
...but as with most technology it's never quite that easy.
Less simple answer, the Mac OS EULA prohibits its installation on non-Apple hardware and Apple will neither offer the OS nor support it on non Apple kit. However there are plenty of OS X installs running on non-Apple hardware; technically it can be done. There are also OS X derived operating systems (such as the Darwin project, originally supported by Apple).
So the real answer is yes you can if you're prepared to accept either questionable legality or something that's OS X-like and *may* run the application you are interested in. Oh and do you want to keep Vista as well?
Suppose you might be able to get OS X running in a virtual machine under Windows? Never tried that - not that I'm suggesting I would have tried any of the above options either

Whether OS X is easier to use than Vista will depend on what you are used to and how easily you adapt to a different operating environment. It's different !
Be interesting to see what FH app your cousin is talking about.
IG