Using MacOS and Windows on one machine is possible, but not as a dual-boot, but one on top of another...
The reason for that is, both OS's (Ooperating Systems) have a different architect and hardware support, so basically if oyu install a MacOS on a Windows, it won't run, and vise-versa.
You can notice this clearly if you visit any Linux site and attempt to download it, you will see that there is a different destribution for each architect.
Ex:
i386, x64, PowerPC, SPARC, etc
PowerPC is the Mac archite created by in 1991 by the Apple-IBM-Motorola alliance, which is also known as AIM.
Installing Windows on a MacOS is possible through Microsoft VirtualPC
http://www.microsoft.com/mac/products/virtualpc/virtualpc.aspx?pid=virtualpc
Otherwise, its installing MacOS on Windows through either VirtualPC or VMware
VirtualPC for Windows:
http://www.microsoft.com/windows/virtualpc/default.mspx
VMware Homepage:
http://www.vmware.com/
VMware Workstation Homepage:
http://www.vmware.com/products/ws/
VMware comes in two releases, one for Windows, and another for Linux, while VirtualPC comes in also, two releases, but one for Windows, and another for Mac.
Hope this answers your question...
Good Luck