{$IFDEF WIN32} 

             function GetVersionEx(lpOs : pointer) : BOOL; stdcall; 

              external 'kernel32' name 'GetVersionExA'; 

             {$ENDIF} 

             procedure GetWindowsVersion(var Major : integer; 

                                         var Minor : integer); 

             var 

              {$IFDEF WIN32} 

               lpOS, lpOS2 : POsVersionInfo; 

              {$ELSE} 

               l : longint; 

              {$ENDIF} 

             begin 

              {$IFDEF WIN32} 

                GetMem(lpOS, SizeOf(TOsVersionInfo)); 

                lpOs^.dwOSVersionInfoSize := SizeOf(TOsVersionInfo); 

                while getVersionEx(lpOS) = false do begin 

                  GetMem(lpos2, lpos^.dwOSVersionInfoSize + 1); 

                  lpOs2^.dwOSVersionInfoSize := lpOs^.dwOSVersionInfoSize + 1; 

                  FreeMem(lpOs, lpOs^.dwOSVersionInfoSize); 

                  lpOS := lpOs2; 

                end; 

                Major := lpOs^.dwMajorVersion; 

                Minor := lpOs^.dwMinorVersion; 

                FreeMem(lpOs, lpOs^.dwOSVersionInfoSize); 

              {$ELSE} 

               l := GetVersion; 

               Major := LoByte(LoWord(l)); 

               Minor := HiByte(LoWord(l)); 

              {$ENDIF} 

             end; 

             procedure TForm1.Button1Click(Sender: TObject); 

             var 

               Major : integer; 

               Minor : integer; 

             begin 

               GetWindowsVersion(Major, Minor); 

               Memo1.Lines.Add(IntToStr(Major)); 

               Memo1.Lines.Add(IntToStr(Minor)); 

             end; 

   Windows API -  функция  

       GetDOSEnvironment() для  Win16 и 

       GetEnvironmentStrings() для Win32. 

Пример :

            procedure TForm1.Button1Click(Sender: TObject); 

             var 

               p : pChar; 

             begin 

               Memo1.Lines.Clear; 

               Memo1.WordWrap := false; 

              {$IFDEF WIN32} 

               p := GetEnvironmentStrings; 

              {$ELSE} 

               p := GetDOSEnvironment; 

              {$ENDIF} 

               while p^ <> #0 do begin 

                 Memo1.Lines.Add(StrPas(p)); 

                 inc(p, lStrLen(p) + 1); 

               end; 

              {$IFDEF WIN32} 

               FreeEnvironmentStrings(p); 

              {$ENDIF} 

             end; 

   Windows API -  функция  

       GetDOSEnvironment() для  Win16 и 

       GetEnvironmentStrings() для Win32. 

Пример :

            procedure TForm1.Button1Click(Sender: TObject); 

             var 

               p : pChar; 

             begin 

               Memo1.Lines.Clear; 

               Memo1.WordWrap := false; 

              {$IFDEF WIN32} 

               p := GetEnvironmentStrings; 

              {$ELSE} 

               p := GetDOSEnvironment; 

              {$ENDIF} 

               while p^ <> #0 do begin 

                 Memo1.Lines.Add(StrPas(p)); 

                 inc(p, lStrLen(p) + 1); 

               end; 

              {$IFDEF WIN32} 

               FreeEnvironmentStrings(p); 

              {$ENDIF} 

             end; 

             procedure TForm1.Button1Click(Sender: TObject); 

             var 

               dc : hdc; 

             begin 

               dc := GetDc(0); 

               MoveToEx(Dc, 0, 0, nil); 

               LineTo(Dc, 300, 300); 

               ReleaseDc(0, Dc); 

             end; 

Вызовите функцию GetWindowsDirectory(). Если Вас интересует каталог System, вызовите функцию GetSystemDirectory().
Пример :

             {$IFNDEF WIN32} 

              const MAX_PATH = 144; 

             {$ENDIF} 

             procedure TForm1.Button1Click(Sender: TObject); 

             var 

               a : Array[0..MAX_PATH] of char; 

             begin 

               GetWindowsDirectory(a, sizeof(a)); 

               ShowMessage(StrPas(a)); 

               GetSystemDirectory(a, sizeof(a)); 

               ShowMessage(StrPas(a));