How to identify the Windows version of a dead install from Linux by having access only to its filesystem? [duplicate]
Simple. Look at the version of <drive>:\Windows\System32\ntoskrnl.exe
In the case of XP, look for <drive>:\boot.ini
If it is Vista+ you can look for the <drive>:\Boot folder.
For Windows 7+ you can look in device manager for the hidden System Reserved partition.
If there is a file named license.rtf in your C:\Windows\System32 folder, it also contains your current Windows version.