is to pay yahoo for the POP3 access. What is it $35 a year or something? I think it also gets you a vanity domain name for the address?
Either that or visit the [link|http://www.freedomlist.com/|Freedom ISP List] and find another ISP that offers free POP3 access?
Are you running Mozilla with the JRE 1.3 runtime? Maybe Yahoo Mail needs Java support?