OK- I had better come clean and admit that I tried to use the Konsole method you recommended , but could not work out how to do the editing. Instead, I opened the file in Konqueror and added the line there. However, I didn't end the file with a new line (I assume that you mean moving the cursor to the line below the added one)- I had no idea that this was necessary. I saved the changes, but noticed that they had not been mirrored in Sudoers~,so I decided it would be best to remove the line and do the job again thru Konsole, once I had done some reading on how to use "vi". After this, the alteration appeared in the back-up file. Since your last post, I've revisited the file in both Konqueror and Konsole and highlighted the line below before saving again.
In answer to question 2--I have been into "Users and Groups" and added robin (myself) and root to the Truecrypt group. One last point- I have always had to use the "kdesu truecrypt" command in Konsole to open the program ; if I try to open it in the normal way, it prompts me for the Truecrypt password, which it accepts, and then for the Administrator password, which it refuses (failed to obtain Administrator privileges)-this is still the case. You could say that my experience with this program has been problematic right from the start!
P.S>I have found that I can get into the drive thru Konqueror in Super-User mode once I have mounted it in Truecrypt-I guess I may have to be satisfied with this.