Slow date comparison

Running Red Hat 7.0 kernel 2.2.16
PostgreSQL 7.0.3
Front End App is Cold Fusion

We only have about 22000 rows in the article table and it will grow quite a bit
larger.
When I turn debugging on (cold fusion) this query takes a while. Almost 3
sec...

rstDispThread (Records=6, Time=2982ms)
SQL =
SELECT a.id_article,
           a.subject,
           getNumPostsInThread(a.id_article,0) AS numPosts,
           isThreadNew(a.id_article,'2001-01-2617:28:37',0) AS  intThreadNew,
           a.is_hidden,
           a.is_locked,
           a.reply_to
      FROM ARTICLE a, USER_TAB ut
     WHERE a.id_article IN (75254,76255,79262,84264,94273,94277)
       AND a.author = ut.id_user
  ORDER BY a.date_create ASC

I have tried numerous indexing techniques and starting up the database with
larger Buffer size, and even the dreaded -F option, but nothing seems to help.

The two functions getNumPostsInThread and isThreadNew are pretty quick. I have
found the date comparison to be slow and was wondering if that could be sped
up?

This is part of the isThreadNew function, when I strip everything out and only
leave the WHERE date_create >=
TO_TIMESTAMP('2001-01-2617:28:37',’YYYY-MM-DDHH24:MI:SS’) clause and only pass
one article id to it - the query still takes .5 sec!! Is there any known
slowness attributed with date comparisons, etc??

SELECT COUNT(id_article)
 FROM ARTICLE
WHERE date_create >= TO_TIMESTAMP('2001-01-2617:28:37',’YYYY-MM-DDHH24:MI:SS’)
 AND (id_article = 79262
OR reply_to = 79262);

Does anyone have any ideas how to speed this up??

I also read something about being able to create an index based on a function
or am I way off base again?

Thanks in Advance,

Rudy Laczkovich