Client connection lost; still in the task list

Hello,

We've just put into production with our main application which we
ported from MSSQLserver to PostgreSQL;

We are overall very pleased with PostgreSQL speed and stability are fantastic.

We have one user which PC keeps freezing and despite rebooting the
computer several times since this morning I can find more than 24
connections for this user when there should be at most 2. So we are
experiencing 'too many users connected' errors

So my question is what makes PostgreSQL realise that a connection is
dead ? when will it drop it and free the connection ?

Doing  a  ps ax  I see many connection related to that IP address,
can I safely kill the processes which are obviously redundant ? if
yes, which signal to send ? (I do not want to kill the postmaster,
just the connection).

Going forward is there a good way of doing this ?

We are running on Centos 4, PostgreSQL 8.3

thanks in advance for your input

Didier