If your or your users' PCs look something like the image pictured here -- geriatric hardware, laughably minimal memory and an operating system that's now three versions old -- Office 2013 isn't in your short-term future. Windows XP and Vista users need not apply. Office 2013, including Office 365, requires Windows 7 or Windows 8. So if you're stretching that XP investment for the foreseeable future, you'll have to stretch an older version of Office, too. Likewise, if you're hoping to mash up an Office 365 subscription with an older version of the desktop software, expect some hiccups with Office 2007.