Unfortunately, libxorg-x11-devel-6.7.0-2mdk.i586, gcc-c++ and some other packages (for example needed for building rpms) are missing on Community CD's, so you should download all of them from any Mandrake mirror.
ftp://ftp.chg.ru/.1/Linux/Mandrakelinux/d...586/media/main/
http://ftp.surfnet.nl/ftp/pub/os/Linux/dis...586/media/main/
be aware and check that package versions are the same with installed in your system