Internet Connection Sharing - an ip nightmare

Hello all,

I'm currently supporting a small charity who have just
opened a sub-office (a classroom in a hut, basically) that
is not connected to their main office's LAN.

In this sub-office there is a windows 2000 Pro PC acting
as an internet connection sharer and a small number of XP
PCs. No problem there.

I have been asked if it is possible to configure a couple
of xp laptops that normally connect to their main lan to
be able to plug in at the sub-office, engage in file
sharing and connect to the internet.

The laptops have dhcp allocated ip addresses (from a w2k
server in the main office) which I suppose would have to
be ditched (registry hack) before plugging in at the sub
office.

They would then need a valid ip address to engage in file
sharing with other machines in the workgroup (which would
need to come from the ICS machine which I understand
allocates ip addresses to clients on the network).

My questions are: I know XP is very good at logging on
with cached credentials - will it be smart enough to allow
log on at the sub-office where there is no domain and pick
up an ip address from the ICS machine???