I can't put more than 16 chars on the Label with NERO 6.3.1.25

I have NERO 6.3.1.25 and when i try to create a new ISO i can't put more than 16 characters on the label.
I'm new with burning cds cause i get my CD/RW yesterday but i really don't know how to change that.
In the compilation properties i have:
File name lenght: Max. of 31 chars (ISO lvl 2)
Format: Mode 1
Character set: ISO 9660
and joliet activated
I also burn a cd a i get "_" instead of spaces in the label.
I know it has to be a way cause i see a lot of cds with more than 16 chars on the label. What should i do???
Thanks
Emiliano
PS: Sry for my english i'm argentinian.