Right ( "0" & Day(datefield ) ; 2 ) will add in the leading zero.
Right ( Year ( datefield ) ; 2 ) will return just the last two digits of the year.
you can use the concatenation operator (&) to "glue" together the parts of your number and still get a number value if you specify "number" as the return type for your calculation (or use a number field with this expression as an auto-entered calculation).
Note: I do not recommend using this value as a primary key in your database.
Fantastic...Thanks Phil. It worked.