You would use primary key (pk in the sample code). Something Like

update ipdatabase.dbo.physicalAddress 
	set physical =  inserted.physical 
	Join deleted on physicalAddress.pk  = deleted.pk 
	Join inserted on physicalAddress.pk = inserted.pk 

>Thats interesting, I've never done a join on a delete statement.
>
>One more question.. How would I handle multiple updates. Right now I have:
>
>

>ALTER   TRIGGER updateMAC ON [dbo].[astudent] FOR  UPDATE AS
>
>/*If the nic column was updated */
>
>if update(nic)
>begin
>	declare @newMAC varchar(16), @oldMAC varchar(16)
>
>	/* Get the new and old mac address */
>	select @newMAC = nic from inserted
>	select @oldMAC = nic from deleted
>
>	/* Update the ipdatabase table */
>	update ipdatabase.dbo.physicalAddress
>	set physical =  @newMAC
>	where physical = @oldMAC
>
>
>end
>

>