VMWare Fusion allows OS X users to run other operating systems as virtual machines without having to resort to other alternatives such as using Apple’s Boot Camp software. The newest VMWare Fusion 4 adds support and optimization for OS X Lion and more than 90 new features.

According to a new support document from Apple, the OS X utility Boot Camp—which allows a Mac owner to run Windows on a separate partition—now allows only Windows 7 to be installed in a fresh OS X Lion installation. This is because version 4 of Boot Camp that comes with OS X Lion requires an authentic 32- or 64-bit Windows 7 Home Premium, Professional, or Ultimate disc.

Today, Parallels announced the availability of their virtualization software Desktop version 4.0. It has a slew of new features, such as Modality, Smart Mount, 64 bit support and Speech Recognition. It’s also said to be 50% faster than version 3.0. You can buy the package for $79.99, or upgrade from version 3.0 for $39.99.

I’ve been using VMware Fusion now for almost a year, but the new features included in Parallels Desktop 4.0 are tempting me a bit to switch. Here’s the breakdown of why I’m tempted…