USB ADSL modem detected only at boot!

[GuruPrasad]

Hello everyone,
Hardware: Compaq Presario 2184 notebook
ADSL modem - connected though USB
OS: Mandriva 2007

My net connection only works when I switch on my modem prior to boot.
(1) In KDE, when the modem is disconnected (physically/switched off) and re-connected, most of the time, the net connection automatically gets re-established. Sometimes, nothing happens, and when I do (as root)

service network restart

I get

Bringing up interface eth2:  usbnet device eth2 does not seem to be present, delaying initialization.           [FAILED]

After which, I have to reboot. Other USB devices, such as my memory stick, continue to be auto-detected after getting this message. I get the same message when I do

ifup eth2

(2) In ICEWM, when the modem is disconnected, I almost always have to reboot to get back online.

I would be very grateful if someone can suggest a way of bringing up interface eth2 without having to reboot the system.
Thanks in advance,

Guru

[GuruPrasad]

Eureka!!
udevstart (as root) does the trick, the modem is detected, and then the network can be reconnected without rebooting (phew!).
when the network was down , lsusb gave:

Bus 001 Device 001: ID 0000:0000

after doing udevstart, lsusb gives

Bus 001 Device 002: ID 0a5c:6300 Broadcom Corp. 
Bus 001 Device 001: ID 0000:0000

Still, I'd like to know why this happens, and I've noticed that sometimes the usbnet device dissappears without any reason. Is there someway I can configure udev so that hotplugging happens smoothly?
Cheers,
Guru