update and select to create a queue

In a queue table we have:

DELETE FROM alert_queue WHERE id = (SELECT MIN(id) FROM alert_queue) RETURNING *

Which allows many processes to get (and process) a single id from the queue table, with no 2 processes getting the same id to be processed.

I would like to do the same kind of thing in a regular table, but with select and update (no delete) - in 1 sql command (no transactions).

Using Postgres 9.0 and Perl DBI,

we have rows of that have a bool column "to_be_processed". I want to get the next  row id  where "to_be_processed" = 'f'  while updating the column to 't' and have many processes running the same query with each getting a separate row (i.e no 2 processes getting the same row).

Quasi SQL:
Update  alert_queue set to_be_processed = 't'  WHERE id = (SELECT MIN(id) FROM alert_queue where to_be_processed = 'f') RETURNING id


Thanks.