alphabet only displays in one line

I've configured the users list enabling the "Provide Menu Tab" box and desabling the "Provide Embedded Menu", so i only have the menu tab alphabet list, but this list displays only in one line going beyond the boundaries of my page, how can i make the line to brake and display the second half of the alphabet in a second line?

You can check what i'm talking about in "http://parles.upf.es/dtf/?q=userlist"

thanks to all.