If you make the directories as root, they should not disappear after rebooting. It seems odd. I use /cdrom as my directory, but I think you can make whatever directory you like as long as it matches what is in /etc/fstab
The second part, if you want to keep using gdm, just select kde from the graphical login manager. It will ask you if you want to make kde the default, or just use it for the current login. The other option is to install kdm
Code:
apt-get install kdm
and select kdm as your default manager. You can select kde as the session when you log in. Kdm automatically uses the previously selected desktop environment on subsequent logins unless you specifically select something different. The advantage of using kdm with kde is that you can shutdown the computer directly from the desktop. If you use gdm and kde, you will log out of kde, then go to gdm and select shutdown, then enter the root password to shutdown. I find it very tedious that way.
By the way, your English is fine. Good luck!