DEFAULT TEXT 'now'

Hi

I´m have a table like bellow:

CREATE TABLE conex (
    id int4 PRIMARY KEY DEFAULT NEXTVAL('seq_conex'),
 
    inicio datetime DEFAULT TEXT 'now', 
    ultimo datetime DEFAULT TEXT
'now',       
                 .
                 .
                 .
)

insert into conex (ip) values(´200.200.200.200´)

Will result every time the same data and time for ´inicio´ and ´ultimo´! 

I want to insert the current date and time. Is that code correct and the
result a bug???
Is there an way to make the DEFAULT work???

I know I can insert like:  

insert into conex (ip, inicio, ultimo) values(´200.200.200.200´, ´now´, ´now´)

but I would like to use DEFAULT.

PostgreSQL 6.4 - Solaris 2.5 sparc

Thank you

Roberto