GamingBolt have discovered
the system requirements for Just Cause 2, highlighting one particular key issue: it will not work on Windows XP. You'll need Windows Vista or Windows 7 and the included fancypants DirectX 10.
While XP support going the way of the dodo was probably inevitable, it's still quite a common operating system for gamers to have installed. No doubt we'll see more and more games follow this path, and even if Just Cause 2 isn't your cup of tea, it's pretty likely that eventually there'll be some game that you want to play that you need to upgrade for. For those - like me - that haven't found any compelling reason to upgrade yet, might be time to start budgeting for an operating system upgrade!