adhoc network 11g wireless dropout woes

wireless setup problems
-----------------------

I'm trying (unsucessfully) to wirelessly network the following kit.

1) Home build pc (athlon 1.4ghz) windows xp connected to ntl broadband
(connection is firewallwed
using zonealarm pro)

2) wireless usb adapter on main pc (
microsoft mn710)

3) laptop (toshiba satellite m30) with built in intel 802.11g running
norton internet security firewall

I've configured internet connection sharing on the main pc and configured
the firewall for ics.

Basically im doing an ad hoc network using ICS. This should work fine
over 802.11g - its
working well over bluetooth. However when i connect using 802.11g (using
WEP encryption)
connection is established and i can even surf for 1 or two pages. However
connection is rapidly dropped -
it usually lasts about 1 minute (maybe less) - longest i would guess was
less than 3 mins. It will
reconnect again only to drop again... really infuriating

ive tried googling for this and not found much of use..
I have ensured that 802.1x auth is disabled and I've run out of things to
try...

Any suggestions would be most welcome.