windows laptop clients

I'm trying to configure several windows xp laptop machines to authenicate with our Mac OS X 10.4.9 Server. It an OD Master and I've set it up as a PDC, the clients can join the domain fine, I've configured both roaming and local profiles and home directories and these are all ok (after a bit of fiddling around). But when I disconnect the laptop from the network and try to log in I get the error message: 'The system cannot log you on now because the domain [domain name] is not available." This is fairly obvious as the laptop is disconnected. Is there a way of caching the authenication details for the user on the local machine so that they can log in offline? - similar to an Active Directory profile? Surely someone out there has tried to configure a pc laptop to authenicate to a Mac network? Any help or advice would be appreciated - Thanks.