Paper Stocks

I am a bit puzzled by the Paper Stock selection, when I go into
File\Print \Paper Stocks 152 predefined stocks are listed.
If I use the drop down list in the main dialog box only 36 are listed.
I would like to know how I can use a stock thats on the File\Print menu if its not on the drop down menu?
Also I wish someone would enlighten me on how the
User Defined paper stock item works, as there is nothing in the help section on this.
Thanks very much for any help.

It might be helpful if you state what program you are talking about.

Sorry about that, the program is the Cover Designer in Nero 5.5