Here's a free Windows emulator for Mac OS X. It's called Darwine and version 0.9.5 is now available for download.
The Darwine project intends to port and develop Wine as well as other supporting tools that will allow Darwin and Mac OS X users to run Windows Applications. There are two major phases to this project.
The first phase is the port of Wine to Darwin/PowerPC with X11 (XFree86).
While the basic compatibility is there as Darwin is largely FreeBSD, there is the hurdle of its Mach kernel which uses the Mach-O format rather than ELF. This part has been achived with success. It means that WineLib is now working on Mac OS X, and that developers should be able to recompile their Win32 Apps using WineLib and make them work in Mac OS X.
The second phase is to then integrate in WINE the QEMU binary translator.
Additional supporting tools for launching Windows applications from the desktop and an integrated installer are desirable items for the package (like OpenOffice is doing).