on install i get this error:

warning: pg_query() [function.pg-query]: Query failed: ERROR: function title(integer) does not exist HINT: No function matches the given name and argument types. You may need to add explicit type casts. in /home/brenda/projects/drupalcore/drupal-5.1/includes/database.pgsql.inc on line 125.
user warning: query: CREATE INDEX five_amazonitem_title_idx ON five_amazonitem (title(100)); in /home/brenda/projects/drupalcore/drupal-5.1/includes/database.pgsql.inc on line 144.

The index isn't created, but the module functions... guess it might get slower later.