"The Wine Project, the community of free software developers dedicated to opening Linux and other POSIX compatible operating systems to Windows applications, today announced the completion of the core architecture for Wine, an open-source project that allows Windows applications to run natively on Linux. Now available as Wine version 0.9, the tools and libraries are functionally complete and ready for commercial testing and optimization."
I've had mixed success in the past trying to run software with Wine, especially because often it was impossible to run the installer for a piece of software. There has been a lot of work in that area, so we'll see.
If you're interested in running Linux apps on Windows (or Linux on Linux or ...), you might want to try out the new free VMWare Player. I installed the viewer for Windows and installed the Browser Appliance, which is a Ubuntu Linux image with Firefox installed. The best thing is that you can update the image to add software, as you can with any Ubuntu distribution (within the limits of the 800 Mb image).
The only major limitation with the player seems to be that you can't create images, but otherwise it works great. I can see it would be useful to try out new software without corrupting an existing install and also for browsing in a 'quarantined' environment. VMWare seems also to be pushing the viewer as something that will help with software distribution. i.e. you make an image with your new software completely configured and give it to a customer with the viewer to run it.
I can see parallels with Adobe's PDF format, which has become very successful because of the presence of a 'free' viewer.