The settings you need are:
Account name: Whatever you like, maybe "Telefonica"?
Name: Your name
E-mail address:
YOURNAME@telefonica.net (I think the name has to be in caps)
Account ID: YOURNAME$telefonica.net (yes, that's a $ sign)
POP server: pop3.telefonica.net
SMTP server: smtp.telefonica.net
HTH