Proper wireless dhcp client setup?

Hello all, this is really 2 questions in one I think.

1. How to properly set up a NetBSD client using an 802.11 network and dhcp.
2. How to do it in my particular situation.

I'm helping my wife's family in the UK set up a wireless network. For
whatever reason, on the short term we've decided to use the home PC
(Win XP) as the "base station". I got a USB 802.11 adapter for it, set
it up ad-hoc, and I have a Windows wireless laptop connected to it and
using the network via "internet connection sharing" with no problems
(first time ever trying that...).

So my questions are the ones above:

1. I can't find any specific document to do this. I have an hpcmips
device which I've had no trouble using with wireless (on a fixed IP
network) or dhcp (on a regular wired connection), but I've never mixed
the 2 before. What I've tried is:

rc.conf:
dhclient=YES dhclient_flags="wi0"

And I've tried booting like that with no manual setup on the wi0 card.
This fails, which is what I would expect because I don't know if the
dhclient knows how to find a wireless network. So then I tried adding
an /etc/ifconfig.wi0 file with just this:

ssid ssidname

Then rebooted, but this doesn't work either.

2. I'm not sure about this Windows sharing stuff, I'm not sure if it's
very robust, so I shut down my Win XP laptop and tried connecting to
this network I set up using just the hpcmips machine (in case the
Windows "base station" can't hand out more than 1 IP at a time? I
dunno...). I still can't get the dhclient to get an address. Maybe I'm
missing something with the Windows networking stuff?

My Win XP laptop is behaving just as if it's getting an address via
DHCP from the wireless network though... I don't know what I'm
missing.

Thanks!

Andy