Finally, go to the package manager in the Mandrake Control Center, section rpm-sources and tick the "updates" box for the update_source.
Now every time you do the updates in the MCC it will look in /mnt/hdaX/MyUpdates if there are new updates available and install them if needed. ( sure, you have to rsync the /mnt/hdaX/MyUpdates first with the command printed above. )
Have fun ! ( and make sure that during all this time the /mnt/hdaX is mounted !! )

Bruno
PS: You can also burn the updates to CD: "mkisofs -R -o Update.iso /mnt/hdaX/MyUpdates" will make an ISO file which you can use to make the UpdateCD. ( See also the second part
Here on how to use the UpdateCD )
-- Mar 06 2006 --