another DECIMAL problem

Hi all,

I'm trying to create an index on a composite key using a DECIMAL type
but PostgreSQL raises the following error:

CREATE TABLE header (
year decimal(4) NOT NULL,
number INTEGER NOT NULL,
date DATE NOT NULL,
cod_client CHAR(4) NOT NULL,
CONSTRAINT k_header PRIMARY KEY (year,number)
);
NOTICE: CREATE TABLE/PRIMARY KEY will create implicit index 'k_header'
for tabl
e 'header'
ERROR: Can't find a default operator class for type 1700.

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PostgreSQL 6.5.0 on i586-pc-linux-gnulibc1, compiled by gcc 2.7.2.1

José