problem with dots in order by

Hello everybody !

I have this order by :
select lalala from tablex order by field_y;
where field_y is a text column.

that returns something like :
2.1004.11
21.00.461
2.1006.21

in  PostgreSQL 7.3.2 in Linux Mandrake 9.1

but in PostgreSQL 8.0.0 in Windows XP it works as I expected ...

2.1004.11
2.1006.21
21.00.461

the two config share the same Encoding when the database was created and
the client enconding is the same in the two cases :

H:\Documents and Settings\User>psql -l -U postgres
        List of databases
   Name    |  Owner   | Encoding
-----------+----------+-----------
 bd2005    | postgres | SQL_ASCII


Can anybody tell me if there is something I can do in the Linux config
to have the same order by result ??
Using XP is only for tests... I love my Mandrake server :P