I paste here some informations. Those files are located in /etc/dbus-1/system.d/ :
NetworkManager.conf :
<!DOCTYPE busconfig PUBLIC
 "-//freedesktop//DTD D-BUS Bus Configuration 1.0//EN"
 "http://www.freedesktop.org/standards/dbus/1.0/busconfig.dtd">
<busconfig>
        <policy user="root">
                <allow own="org.freedesktop.NetworkManager"/>

                <allow send_destination="org.freedesktop.NetworkManager"/>
                <allow send_interface="org.freedesktop.NetworkManager"/>
        </policy>
        <policy user="haldaemon">
                <allow send_destination="org.freedesktop.NetworkManager"/>
                <allow send_interface="org.freedesktop.NetworkManager"/>
        </policy>
        <policy at_console="true">
                <allow send_destination="org.freedesktop.NetworkManager"/>
                <allow send_interface="org.freedesktop.NetworkManager"/>
        </policy>
        <policy context="default">
                <deny own="org.freedesktop.NetworkManager"/>
                <deny send_destination="org.freedesktop.NetworkManager"/>
                <deny send_interface="org.freedesktop.NetworkManager"/>
        </policy>

        <limit name="max_replies_per_connection">512</limit>
</busconfig>


nm-applet.conf
<!DOCTYPE busconfig PUBLIC
 "-//freedesktop//DTD D-BUS Bus Configuration 1.0//EN"
 "http://www.freedesktop.org/standards/dbus/1.0/busconfig.dtd">
<busconfig>
	<policy user="root">
		<allow own="org.freedesktop.NetworkManagerInfo"/>

		<allow send_destination="org.freedesktop.NetworkManagerInfo"/>
                <allow send_interface="org.freedesktop.NetworkManagerInfo"/>
	</policy>
	<policy at_console="true">
		<allow own="org.freedesktop.NetworkManagerInfo"/>

		<allow send_destination="org.freedesktop.NetworkManagerInfo"/>
                <allow send_interface="org.freedesktop.NetworkManagerInfo"/>
	</policy>
	<policy context="default">
		<deny own="org.freedesktop.NetworkManagerInfo"/>

		<deny send_destination="org.freedesktop.NetworkManagerInfo"/>
		<deny send_interface="org.freedesktop.NetworkManagerInfo"/>
	</policy>

        <limit name="max_replies_per_connection">512</limit>
</busconfig>


nm-openvpn-service.conf 
<!DOCTYPE busconfig PUBLIC
 "-//freedesktop//DTD D-BUS Bus Configuration 1.0//EN"
 "http://www.freedesktop.org/standards/dbus/1.0/busconfig.dtd">
<busconfig>
	<policy user="root">
		<allow own="org.freedesktop.NetworkManager.openvpn"/>
		<allow send_destination="org.freedesktop.NetworkManager.openvpn"/>
		<allow send_interface="org.freedesktop.NetworkManager.openvpn"/>
	</policy>
	<policy context="default">
		<deny own="org.freedesktop.NetworkManager.openvpn"/>
		<deny send_destination="org.freedesktop.NetworkManager.openvpn"/>
		<deny send_interface="org.freedesktop.NetworkManager.openvpn"/>
	</policy>
</busconfig>

The other nm-[vpnc-service|ppp-starter] are like the latest one.

According to the error reported by nm-applet when launching it through
nm-applet
in a shell :
** (nm-applet:13017): WARNING **: <WARN>  nma_dbus_init(): could not acquire its service.  dbus_bus_acquire_service() says: 'Connection ":1.44" is not allowed to own the service "org.freedesktop.NetworkManagerInfo" due to security policies in the configuration file'

there's an error in the rights defined for "org.freedesktop.NetworkManagerInfo";
I'm going to try to change rules in NetworkManager.conf and nm-applet.conf, allowing ALL in "default" section. Maybe it's unsecure, ugly and so on... but if it works, my Boss will be really pleased.

The really strange thing is, I installed a laptop (dell latitude d620) 2 days ago, under gutsy, but this one doesn't have this problem.
I can say it's NOT a problem only on my Boss' laptop, as a workstation do have it too (but this one is upgraded to Hardy now).

I'm also going to read configurations on the old d620, maybe there will be a hint in it....

I'll post results here when I have them.

Regards

C.