Could not create a table named "USER" under postgreSQL

Hello,

I have a question about "date" & "timestamp" types in PostgreSQL. I want
to setup the default value '0000-00-00' and "0000-00-00 00:00:00" for
them. However, it seems that PostgreSQL does not support it. Could
someone helps me please?

The example table:

T1 (col1      varchar(7) not null,
    col2      varchar(4) not null,
    col3      date not null,
    col 4     varchar(3),
    primary key(col1, col2, col3)
)

In my design model, "col3" has to be one of the primary key part. Since
at the beginning of the data population, we do not know the value of
"col3"; values for "col3" are input throught GUI. Therefore, when I use
MySQL, the default values I gave is "0000-00-00". However, after I
migrate to postgreSQL, I could not setup the default values as
"0000-00-00" any more. Could somebody help me about it please? I'd like
to know how I can save '0000-00-00' as the default value for "date" and
"timestamp" types.

By the way, I also tried "my2pg.pl" to migrate table structures got by
mysqldump to postgreSQL. The places I have '000-00-00' have been changed
to '0001-01-01' by this perl script.

Thanks a lot in advance,
Emi Lu