Is there any system for adding addresses to e-mails in g-mail like there is in Yahoo and MSN mail?

Can you be a bit more specific? Are you talking about adding a signature or adding address information to contacts?

Adding address information.
Log in to your Gmail account.
Click Contacts on the left side of any Gmail page.
Click the name of the contact you'd like to edit.
Click edit contact information.
Click add more contact info
Edit the desired field(s).
Click Save.