Parallels Workstation allows you to run any Windows software in a window on your Intel OSX Mac transparently as though the apps were Mac apps. With Parallels you can share files back and forth between PC and Mac. You can use the BootCamp created WindowsXP partition or you can use a virtual hard drive file that if it gets infected with a virus or spyware you can simply trash and revert to a clean copy.
Apple’s BootCamp allows you to repartition your HD to install a bootsble copy of WindowsXP or Vista that allows you to run your Mac as a Windows PC at full speed. Many PC pundits have reported that a Mac is the fastest Windows PC they have ever used! Parallels and Fusion will do the same thing in a Mac window under OSX with only a 5-10% speed hit.
You can also use VMWare’s Fusion to accomplish the same thing.
Now, I know the answer to #3. A Mac OSX app called Reunion is GEDCOM compliant and can access the standard geneology files used by almost all geneology programs.
You'll want to use WMWare, not Parallels, for doing this. The features are similar but WMWare images are solid and error-free. Parallels images tend to become flaky and hard to start with time, and the virtual disks develop flaws that cause your Windows image to "bluescreen".