strange slow performance

Hi !
I have a strange slow performance problem depending on client computer.
I have a postgresql server (8.1.3) running on an XP system (P4 3GHz,
1Go RAM).

I have 3 other computers from which I make request on the database : 2
XP(named 1 & 2) and 1 2K.

>From one XP(1) and from the 2K computer, I have no slow performance
problem. I ask for a select of 4000 records, the request is processed
in less than 1 seconde.
>From the last XP (2) computer, the same request takes more than 10
seconds. From this computer I have no other network problem, I can
copy, paste network files without any performance problem.

The 3 clients use odbc driver 8.01.02.00.

I tried to install the postgre sql server on the xp (2) and make the
same request from 3 other computers : no problem, the process takes
less than 1 second from all clients

what goes wrong ??
thanks for your help

Mike