Category No. 2: Emulate a PC
This is the best approach for most users, since it means that they don't need to leave the Mac world to use Windows software; instead, Windows runs in a virtual machine. However, there are downsides: the software costs money, you don't get the 99.99 percent compatibility of Boot Camp, you need lots of RAM (2 GB is a minimum, 3 is better and 4 is comfortable), and there's more complexity for the user as a result of running two operating systems at the same time.
There are two very good, reasonably-priced emulation packages, VMWare Fusion and Parallels Desktop, which permit Mac users to use Windows applications right alongside their Mac applications. Their feature sets and general functionality are very similar, and they keep leapfrogging one another in terms of capabilities, with both having recently released major new versions. While either product will get the job done quite nicely, the conventional wisdom suggests that VMWare has somewhat superior performance and hardware emulation abilities, while Parallels Desktop offers better overall integration into the Mac OS X environment.
Either product will guide you through a streamlined Windows installation and leave you with a fully-functioning virtual machine. To really integrate with the Mac, get everything set up for the user in either single-window or full-screen mode. Open any common applications the user will be using and they will appear in the Mac dock. Right-click on them and choose "Keep in Dock."
Then activate Coherence mode (Parallels Desktop) or Unity mode (VMWare Fusion), which will hide the Windows desktop, and instead allow Windows' windows to sit freely on the Mac desktop, alongside the Mac windows. The user can just click on his Windows shortcuts in the Dock to get to the Windows apps. (If the user feels uncomfortable not being able to see the Windows desktop, then he should stick to single-window or full-screen mode.)
Both products also offer the ability of treating a Mac folder as a network drive, and designating a drive letter for it. I highly recommend setting this up for the user's Documents folder and advising that all documents be saved to it, rather than the C: drive. This way, all documents are accessible on the Mac side as well, and not "locked" inside the large hard drive file which represents C:. Further integration capabilities of both VMWare Fusion and Parallels Desktop are impressive, deep and beyond the scope of discussion here, but you'd be well advised to spend some time on your own machine getting to know each product. Both offer fully-functional trial demos for download.
I should note that other PC emulation products exist, including the recently-released, free VirtualBox from Sun Microsystems. However, Parallels Desktop and VMWare Fusion are the most mature and widely used. But if you're feeling adventurous, by all means feel free to try another product.
Category No. 3: Support Windows software
An interesting option is CodeWeavers Crossover Mac, which is a polished version of the Wine emulator often deployed by Linux users. Rather than emulating a full PC, Crossover Mac instead emulates the Windows application APIs, allowing Windows applications to run on a Mac without actually running under Windows. The advantages are that it's simpler than emulation and you don't need to install Windows at all.
The downside is that compatibility under Crossover Mac is dramatically less than the first two options, making it better suited for running applications that are known to work (for example, Outlook 2007). CodeWeavers maintains a compatibility list on their Web site. But if an application doesn't appear on the list, that doesn't mean it doesn't work, so you might want to try it out.
The moral of the story here is that your Mac users don't need to be left out from the world of Windows software. No longer will your organization's customized Windows software be the reason your users can't switch from Mac to PC. There are many options that enable you to provide them with the best of both worlds.