See changing the e-mail program used by Firefox for how to setup Firefox to use Outlook Express.

Thanks works perfectly.

Do you know if I can put a mail button onto the task bar in Firefox in the same way as on Internet Explorer

You can add a button by using the Get Mail add-on.

The host 'yahoo' could not be found. Please verify that you have entered the server name correctly. Account: 'yahoo', Server: 'yahoo', Protocol: SMTP, Port: 25, Secure(SSL): No, Socket Error: 11001, Error Number: 0x800CCC0D is what it say when i try to use outlook express

Thanks again. Hopefully thats me sorted out, at least for now.