There are no emulators for Windows on modern Macs. Modern Macs leverage Intel Virtualization technology, which is about a billion times better than the old PowerPC x86 emulation attempts.
VirtualBox from Sun is free (as in free), and works very well running pretty much any version of Windows you wish.
With VirtualBox, I can run pretty much any software I need to program or control a scanner. You have to be careful when using USB devices, and ensure when plugged in the Virtual Machine "captures" it, but otherwise I have run Win500, ProScan, Uniden Sentinel, FreeSCAN, almost all of the GRE/Whistler/RS iSCAN/ezSCAN programs, and many others.
Most developers have no interest in writing for the platform, and with the introduction of Intel Macs and Virtualization, have even less incentive to do so now. You could buy almost any junky $199 BigLots PC out there, and accomplish the same thing. Taking into consideration you will need a legit copy of Windows, it may be a better solution.