date comparisons

This should be simple but I am missing something. I am trying to extract
all records entered after a given date. The table has a field
date_entered which is a timestamp. In this particular case I am not
worried about time.

I have tried:
select id from main_table where
date_entered > to_timestamp('January 2006', 'Month YYYY');

select id from main_table where
(to_timestamp('January 2006', 'Month YYYY'), now()) overlaps (date_entered, date_entered);

Both of these return all the rows in the table. Half of the rows are
dated 2000-06-22 12:00:00.

PostgreSQL version 8.1.4

What am I missing?
Belinda