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;