This will not work if you still want to login to yahoo's email site. You need an email account that supports the IMAP protocol. POP accounts do not support 2-way communication, meaning it doesnt work for syncing across multiple devices (such as PC + your DROID).
For example, if yahoo is set to froward all new mail, but also keep a copy on yahoo site. You could then read/delete the copy left on the yahoo site, but that would not update with your droid phone.
This is why you need to forward email to GMail, and use the GMail website to check the forwarded mail.