Waa....I'm confused. Are you trying to log in from the XP maching to Samba, or the other way round? It sounds to me as if you're trying to log in from Linux Samba client into XP, and don't want to put in a password, correct? If so, then just specify "-o password=".
I might, of course, be interpreting the question entirely incorrectly, in which case I apologise in advance.