How to Get Windows OS Version ?

Here's how to get the Windows version from Delphi code:

type TWinVersion = (wvUnknown, wvWin95, wvWin98, wvWin98SE, wvWinNT, wvWinME, wvWin2000, wvWinXP, wvWinVista) ;
...

function GetWinVersion: TWinVersion;
var
  osVerInfo: TOSVersionInfo;
  majorVersion, minorVersion: Integer;
begin
  Result := wvUnknown;
  osVerInfo.dwOSVersionInfoSize := SizeOf(TOSVersionInfo) ;
  if GetVersionEx(osVerInfo) then
  begin
    minorVersion := osVerInfo.dwMinorVersion;
    majorVersion := osVerInfo.dwMajorVersion;
    case osVerInfo.dwPlatformId of
      VER_PLATFORM_WIN32_NT:
      begin
        if majorVersion <= 4 then
          Result := wvWinNT
        else if (majorVersion = 5) and (minorVersion = 0) then
          Result := wvWin2000
        else if (majorVersion = 5) and (minorVersion = 1) then
          Result := wvWinXP
        else if (majorVersion = 6) then
          Result := wvWinVista;
      end;
      VER_PLATFORM_WIN32_WINDOWS:
      begin
        if (majorVersion = 4) and (minorVersion = 0) then
          Result := wvWin95
        else if (majorVersion = 4) and (minorVersion = 10) then
        begin
          if osVerInfo.szCSDVersion[1] = 'A' then
            Result := wvWin98SE
          else
            Result := wvWin98;
        end
        else if (majorVersion = 4) and (minorVersion = 90) then
          Result := wvWinME
        else
          Result := wvUnknown;
      end;
    end;
  end;
end;