How do i create a table in mysql that is dependant on another table but can be one of 3 different tables but not belong to either of the others

in all honesty the way i described it was terribly worded, however this image describes what i am wanting to do fairly clearly.
http://img406.imageshack.us/img406/9732/testvh8.png

The d was added from mspaint, i remember them from my database design class but now i fear that mysql does not support them and i'll have to make some major design changes

This example may help:
http://blogs.conchango.com/davidport...-Subtypes.aspx

that looks like exactly what i am looking for, thanks