This is off the top of my head - I have done this but it has been a long time - but here goes:
1. I seem to recall that the passwords _have to_ be encrypted.
2. Have you added a smb user on the linux box? I added a user in the usual manner and then had to give him/her a samba password thusly:
# smbpasswd -a username
The '-a' is key first time around as it 'adds' the passwd for the user.
3. The above user should be the same name that is used in windows to log in for MS networking. This is because smb is patched onto *nix which requires usernames and passwords while MS only needs the password. (Your MS username gets passed to the samba box and this is used to determine if there is something there that you are allowed to see.)
4. You will need to have set up some shares - 'homes' might be the easiest for a start so you can see if everythings working.
I don't know if any of this helps - I'm assuming a lot since you only posted a small bit of info - I'm assuming that you are going through the same process that I did I guess. (process = mistakes)
Some of the real gurus can probably straighten out anything that I got wrong - I hope.