How can I change my e-mail address for Outlook Express?

It depends what your e-mail address is.

You need, first to get a new e-mail address that uses POP3 and SMTP protocols ( I think Yahoo addresses don't allow that.)

You then need to go into Outlook express, and find the "account" option in the tools menu.

You then have to follow the instructions, putting in your address, password, etc. (not forgetting the POP and SMTP addresses)

and voilà, you have a new address.

Now, when you create a new message, you can choose (with a drop down menu) the address you want to use.

Hope that was clear enough !!

Make outlook your default e-mail.