Dual usage of Outlook and web-based mail

I did a reformat and reinstall on a client’s computer, a Gateway Essentials 550, P3-550, 128 MB, etc. She previously was set up to load email across a DSL line to both pacbell.net (a Yahoo! isp) and Outlook. I don’t know much about Outlook. I have the email coming to pacbell.net ok, but have not been able to configure Outlook properly. Am setting it up with her name, her email account name, etc., and showing mail.yahoo.com as incoming POP3 and smtp.yahoo.com as outgoing. These parameters are allowing neither outgoing nor incoming. I know I’ve got it wrong, but I don’t know how to fix it. Any suggestions?