how to INSERT foreign keys?

I have an <items> table, and a <keys> table, and a map table that relates
item_id's to key_id's. How do I populate item_keys with data?

I tried:

INSERT INTO item_keys SELECT item_id from items where item = 'item 1',
SELECT key_id from keys where key = 'key 1';

but the parser doesn't like that.

Thanks!