Maybe you’d rather just dip your toes in the Windows 8 waters, and not go all the way in. Totally fine. You can install a partition and run Windows 7 and Windows 8 side-by-side and even select which is the default.
If you’re starting from Windows 7, just go to Windows’ Disk Management and set up a 20GB partition for Windows 8. From there, you can simply install Windows 8 on that partition. You can use the aforementioned boot drive selector in Windows 8 to pick which OS you’d like to make the default.