Equally important, don't assume that you'll be able to get everything for free. Every major Linux distribution offers repositories of free open source applications that can often be worthy substitutes for commercial Windows software. Occasionally, however, purchasing commercial software for Linux may be the only adequate solution.
The ability to integrate Linux desktops with essential back-end systems and business processes will be crucial to your success. As a general rule, it is easier to support administrative staff on Linux than so-called knowledge workers, but even a front-desk receptionist will need access to certain core capabilities.
Take e-mail, for example. Basic messaging should be no problem under Linux, but more advanced groupware functionality -- such as shared calendaring -- presents a bigger challenge. IBM offers a Lotus Notes client for Linux, and the open source Evolution mail client can integrate with Exchange Server, but neither solution is likely to sit well with groupware power users. And forget about SharePoint; Linux users are shut out.
Linux-friendly messaging and collaboration servers do exist, but switching may not be a realistic option. The business risk associated with replacing a heavily loaded Exchange Server may simply be too great. Also, inadequate integration with Active Directory, for example, can hamper Linux in a corporate environment.
Frustrations like these are inevitable: This is vendor lock-in at work. As a general rule, the leading Linux applications support most of the functionality that users expect from their categories, but proprietary protocols and closed APIs can thwart true compatibility. To expect a one-to-one replacement for every feature of a specific commercial application would be unrealistic.
The same holds true even for basic desktop productivity software. For example, Linux applications handle files saved by Office 2003 and earlier well, but they still lack support for the newer Office 2007 file formats. You'll need to examine the actual workflows within your organization carefully to determine whether it will be feasible to migrate away from Office. Ask tough questions.
Bridging Windows and Linux
You may find that certain employees rely heavily on specific Windows software for which there is no adequate Linux equivalent. In such cases, you have several choices, though none is ideal.
One option is to configure desktops as dual-boot systems, which allows the user to select either Linux or Windows from a menu at startup. This isn't very efficient, however, and it can also be problematic; for example, files created under Windows will be accessible from Linux, but not the other way around. Don't be surprised if users lapse into old habits and spend most of their time in Windows.