Point your desktop Web browser to this link: https://bis.na.blackberry.com/html?brand=rogers
Click on Create New account
In the process you'll have the option to specify what email address you would like to add to it- enter your Yahoo email address and password.
You are done. It is that easy.
If you managed to create blackberry email address in the process- delete it.
As for Hotmail- adding it to blackberry is hit and miss. Try it anyway, the process is easy.