Not that I've heard.  Although they both use Intel CPU's, that's about as far as it goes.  Same way you cannot load Windows on a MAC directly.  You can load Windows under the MAC OS but not directly.

 

One thing to consider, Apple designs both the hardware and software (Operating System) and the software is designed to only work with the Apple hardware.  This is the reason MAC Operating Systems do not have many of the problems of the Microsoft Operating systems that have to be designed to work on thousands of potentially different hardware configurations.

 

One thing ironic, there have been reports that some MAC users are experiencing the "Blue Screen of Death" installing the new MAC Leopard OS.  Click Me 

I'll take it back that a MAC OS can't be installed on a Windows PC.  I just saw an article where someone hacked Leopard and installed it on a PC.  However, as that is beyond the terms of use of the forum that's all I can (I hope) say about it.