Cascading combo boxes - are they able to do this?

I would like to set up a form containing a combo box with a list of
mechanisms of injury. Some mechanisms have sub groups that I would like to
have visible by means of linking them with a cascading combo box. Is it
possible to have only some records from Cbo 1 link to Cbo 2? The examples I
have seen to date show cascading data for all records in the first combo ie
the city/state or postcode/suburb examples where every record has a sub
record.

Thanks for your help.
--
Joe