Inserting float with ',' instead of '.' using COPY statement

Hi all,
I'm a new user of postgresql. I haven't problem to install and execute postgresql 7.1.3 on my Linux 7.1.
But I don't able to insert a float number with comma separator for decimal, for example:

CREATE TABLE test (
field real
)

INSERT INTO test values ('2,5')\g

ERROR: bad float4 input format

if I write:
INSERT INTO test values ('2.5')\g then all works fine.

Can someone help me to configure postgresql to accept ITALIAN number format?

Thanks in advance at all.

Pier Paolo.