You Can Use PC Disks in Mountain Lion
One of the most excellent features of OS X Mountain Lion (if you have friends unfortunate enough not to own Macs, and you want to share files with them) is that it reads and writes CDs and DVDs that can be read by PCs.
Although your Mac can read disks formatted by a PC, the files on them might or might not work for you. If the files are documents, such as Microsoft Word or Microsoft Excel files, one of your Mac programs can probably open them.
If the files are Windows programs (these often sport the .exe extension, which stands for executable), your Mac can’t do anything with ’em without additional software designed to run Windows programs.
So if you want to run Windows on your Mac, you need to use either Mountain Lion’s built-in utility called Boot Camp or a third-party program such as Parallels Desktop from Parallels, Fusion from VMware, or the free VirtualBox.
Boot Camp requires you to reboot your computer each time you want to use Windows; the third-party programs emulate PC hardware so that you can run genuine Microsoft Windows operating systems in Mountain Lion without rebooting your Mac.
So with a commercial app such as Parallels Desktop or VMware Fusion, the free VirtualBox from Oracle, or Mountain Lion’s included Boot Camp utility, your Mac can run those .exe files (which is to say most Windows programs).
None of these comes with a copy of Windows (required).
Parallels Desktop and VMware Fusion are almost as fast as a PC when running most Windows applications. Depending on which Intel-based Mac you have, they might even be speedy enough to play first-person shooters.
Boot Camp is even faster but has the disadvantage of requiring you to leave Mountain Lion and restart your Mac before you can use it. For most other stuff (including the Windows-bundled Solitaire), all three are capable of running Windows a heck of a lot faster than many PCs are.