Upgrading to Windows 8 is going to be super cheap if you're on Windows XP, Vista or 7. It'll only cost $40 bucks.
The $40 upgrade price for Windows 8 Pro is part of an upgrade extravaganza promotion period lasts from the Windows 8 launch until January 31st, 2013. It will give you a step by step instructions on how to download and check to see if your PC meets with the system requirements.
It's going to be really affordable to upgrade, so why the hell not.