hmm..
this problem may have been of my own making.
i have made serveral unsusseful attempts to install gnome until I finally convinced myself that KDE is not that bad.
And if Patrick hasn't geared slack 4 it then i'm not gonna try and shoe horn it in.
So the /usr/bin/gdm file and the files that the gdm script point to( i.e gdm-start )are still on my system?!??
Anyway I have commented out the reference to gdm from rc.4,so thank you very much for your pointer.
kdm as the next default in the script starts up ok.
cheers