Efficiently move data from one table to another, with FK constraints?

I am using COPY to bulk load large volumes (i.e. multi GB range) of data to a staging table in a PostgreSQL 8.3. For
performance,the staging table has no constraints, no primary key, etc. I want to move that data into the "real" tables,
butneed some advice on how to do that efficiently. 

Here's a simple, abbreviated example of tables and relations I'm working with (in reality there are a lot more columns
andforeign keys). 

/* The raw bulk-loaded data. No indexes or constraints. */
CREATE TABLE log_entry (
    req_time TIMESTAMP NOT NULL,
    url TEXT NOT NULL,
    bytes INTEGER NOT NULL
);

/* Where the data will be moved to. Will have indexes, etc */
CREATE TABLE request (
    id BIGSERIAL PRIMARY KEY,
    req_time TIMESTAMP WITH TIME ZONE NOT NULL,
    bytes INTEGER NOT NULL,
    fk_url INTEGER REFERENCES url NOT NULL,
);

CREATE TABLE url (
    id SERIAL PRIMARY KEY,
    path TEXT UNIQUE NOT NULL,
);

Is there a way to move this data in bulk efficiently? Specifically I'm wondering how to handle the foreign keys? The
naiveapproach is: 

1) For each column that is a foreign key in the target table, do INSERT ... SELECT DISTINCT ...  to copy all the values
intothe appropriate child tables. 
2) For each row in log_entry,  do a similar insert to insert the data with the appropriate  foreign keys.
3) delete the contents of table log_entry using TRUNCATE

Obviously, this would be very slow when handling tens of millions of records. Are there faster approaches to solving
thisproblem?