Logging onto domain whilst disconnected

[Matthew]

I use a laptop to connect into my company's network using
VPN software.
What I would like to be able to do is log in from home on
the laptop using the following account:
domainx\matthew doe
When I try that, I get the message:
'The system could not log you on now because the domain
DOMAINX is not available'

If I were to take my laptop into work, physically connect
to the network there and log in, then my account details
would be cached and next time I logged in disconnected I
would be OK in the above scenario. I would log in, then
start the VPN software and would be fuuly connected as
the above-named user.

So, here's the question. Is there any way to persuade XP
to cache my login details without physically making the
(long) journey to the company office?

Please note that:
(a) The laptop *is* already joined to the domain.
(b) I *can* log in as a local user on the laptop, then
fire up the VPN software and get full access to the
domain resources.

Thanks in advance for any help with this one,

--Matthew