Passwords do not get passed in clear text.. They did 15+ years ago, but that's been addressed now. I just ran a capture on my linux server mounting an xp share - I can see the user name, share name, client version, etc. But the password is hashed using a challenge / response algorithm. Each time you connect, the password hash is different. Passwords for CIFS mounts can NOT be sniffed off the network.
You MIGHT be able to configure everything to force clear text passwords, but I highly doubt it.