I'm a happy Windows 7 user, but I know some people are sticking with Windows Vista or XP. Did you like the new features that Microsoft has been showing off in Office 2013? If so, you're going to have to upgrade to at least Windows 7 to enjoy it.
On the official Microsoft Office 2013 required specs page, the company confirmed that Office 2013 will only work on Windows 7, Windows 8, Windows Server 2008 R2 and Windows Server 2012. It's kind of a sneaky way of getting people to upgrade their computer, but that's just how it goes.
As for the other requirements, Office requires at least a 1GHz or faster x86 or x64 processor with 1GB of RAM on 32 bit and 2GB of RAM for 64 bit. It only requires a modest 3GB of hard drive space so nothing too intense there. One thing that may have forced the move away from XP is that Office 2013 also requires a graphics chip that is at least capable of Direct X 10, which is only available for Vista onwards.
Upgrading from XP is probably for the best anyway. Microsoft has officially stopped supporting the platform with regular security updates and Vista is on its way out as well. An upgrade should be in the cards anyway for the number one users of Windows machines - Enterprise customers. You get the latest security updates and be able to use Office 2013. It's a brilliant strategy on Microsoft's part even if it is a little underhanded.
If you find that you must have Office 2013, there are a few options available to you. The easiest is that people on Windows XP or Vista machines can upgrade to Windows 8 for only $40 through a digital download once it launches on October 26. Some XP computers are too old to even run Windows 8 so it's probably better to just buy a whole new computer at that point.[h/t: CNET]