You might be able to do that using a mail prgram like outlook, I doubt you can do it on webmail (in a web browser) but could easily be wrong.
You need the server settings for aol mail and for yahoo mail:
http://email.about.com/od/accessingaolmail/f/AOL_Mail_SMTP_Settings.htm
I dont know if those infos are current.
You'll probably need a guide as well:
http://classroom.synonym.com/forward-incoming-emails-aol-14400.html
Good luck.