Identificar versão do Windows pelo Delphi

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;