Foreign Keys Help Delete!

DB: Postgresql 7.0.2
OS: Solaris 2.6

Schema:
    hosts table with fqhn column
    routes table with fqhn foreign key hosts(fqhn)

Problem:

1. When I try to change fqhn in hosts, it complains that
I have now violated entry in "routes" table.

2. When I try to update "routes" table, it updates.

3. Go back to "hosts" table and now try to rename/delete
old fqhn and it complains about object missing with OID=xxxxx.


Questions:

1. What's the proper way to delete foreign keys?
(I can dump the DB, edit it, and restore it, but that is
not effecient!!)

2. How can I avoid problems such as above, besides not
using foreign keys?

3. Are foreign keys broken in pg7.0.2???

TIA
tim
dirac@applink.net