Determining windows version at runtime

Sorry if this is a simple question, I am totally new to Windows programming 🙂

I am packaging an installer which only requires a reboot if the Windows version is XP.

I can't see an inbuilt constant for Windows version in NSIS, what's the easiest way to get this from the system? Some arcane registry key?

thanks,

N

Inlcude WinVer.nsh and use ${If} ${AtLeastWinXP} and friends.

Too easy, thanks.