It's no secret you can run various flavors of Windows on Intel Macs using Apple's Bootcamp or other popular virtualization software options like Parallels Desktop and VMware Fusion. Any of these work great if you need to run Windows software on your Mac or even test beta software worry free, but a fairly recent discovery of mine might be a better choice. VirtualBox is the free, cross-platform, open-source virtualization software I used to get the Windows 7 beta running on a Mac, and it just received a major update.
VirtualBox 3.0 (Windows or Mac) lets you create a secure virtual environment to run the OS of your choice without effecting anything else on your computer. This means that in addition to being able to run software meant for a different system, you'll also be able test beta software without fear of conflicting with your current regular setup.
The new version of VirtualBox offers a huge laundry list of new features and fixes, but the major version updates include the capability to run up to 32 virtual CPUs; run programs (games!) that require Direct3D 8 or 9 (Windows); and newly added support for OpenGL 2.0 for Windows, Linux, and Solaris.