Icehouse: Composite Foreign Keys asks a question that I think will interest many:
The SQL book says nothing about this situation... only shows single field foreign keys referencing a single table and multiple field foreign keys referencing a single table.
Just as you made composite primary keys, try the following type of alter table command:
alter table NAME_OF_TABLE add foreign key (KEY1, KEY2) references TABLE_KEYS_FROM;
Make sure KEY1 and KEY2 are exactly defined as in the original table and are in exactly the same order.