I've used Win4LinPro, still do, actually, and VMware Workstation. If all you want is a fast&dirty Windows installation for a single application, and you have the necessary license for Windows, until now, in my opinion, WinPro was the way to go.
VMware is much more versatile, allowing for the installation of multiple OS systems, but launch of VMware, and then whichever OS was slow if all you needed was a single application.
Now, for the past couple of weeks, I've been playing with VirtualBox 1.6.2. Wow! Since Sun took it over and did their rework on it, it is really fast and easy to install and use. Sorry, VMware, but it's true. VirtualBox is every bit as versatile as VMware, and it's faster to launch, and less processor hungry while running than VMware. And WinPro has become rather like driving a 53 chevy. It works, and it hasn't given me any problems, but that is where the positive comments for me end regarding WinPro.
I probably won't toss WinPro out, since I'm basically cheap, and I hate to toss anything that I paid for. Same for VMware Workstation, bought and paid for, but I probably won't toss it. That said, however, I'll probably uninstall both of them and just keep the installers around just in case.
I'm really that impressed with VirtualBox.

owa

Agree with you, just installed virtualbox today and with seamless integration. It is pretty cool and like you said loads fast.

Need to test how it handles under pressure to give it both thumbs up.
Have you tried Xen ? I've been meaning to test it out and see how it compares to vmware and virtualbox.


Uxinn