Do you want to try Windows 8 already? Microsoft released a Developer Preview of the next version of Windows. I will recommend to install this system on a new partition on better in a virtual machine. Virtual Box is free virtual machine and support Windows 8.
First step, Download the appropriate Windows 8 ISO from the Microsoft Developer Network site, burn it to a DVD if you want to install on a test computer or in a new partition.
Install on a New Partition
To create a new partition on Windows Vista or 7, you have to open Control Panel and then Administrative Tools. Double-click on the Computer Management option. When that window appears, look for the "Disk Management" submenu under "Storage" on the left-hand sidebar.