For many of us, running Linux as our full-time desktop OS sounds appealing, but there are always those one or two Windows-only programs that we simply can't do without. Sure, you can switch to Windows using a dual-boot system, or run Windows inside virtualization software such as VMware; but that means filling up your hard drive with two separate operating systems, both of which require regular maintenance. Worse, you'll still need to buy a copy of Windows.
Wine is different. It allows you to run Windows software on your Linux desktop as if it were native Linux software. You don't need a virtual machine; in fact, you don't even need a Windows license. The Wine software is so unusual that the first stable version -- Wine 1.0, released Tuesday -- was a full 15 years in the making.
What the Wine developers have done is write a "clean room," work-alike implementation of the Windows APIs for Linux. In other words, they let Linux speak Windows' language. When an application tries to make a Windows system call, the Wine libraries intercept it and perform whatever action was requested -- only they do it the Linux way, instead of the Windows way. The result is that the applications do what you expect them to do, even though they aren't running on Windows.
Does it sound too good to be true? Well, nobody's perfect. Wine won't run every Windows application out of the box yet (and some might never be supported). If you're curious as to what works and what doesn't, you can consult the application database to check the status of any of the thousands of apps that have been tested with Wine so far.
As a general rule, the more modern the application, the less likely it will run well under Wine (because the developers have had less time to address any problems). But Adobe Photoshop CS2 is listed under "platinum status" -- meaning it installs and runs flawlessly -- so don't assume that only rinky-dink apps will work. Also, if your business has specific application needs, a company called CodeWeavers markets a product based on Wine called CrossOver Office, which includes commercial support.