To test if your Linux machine sees the shares on the Windows box:
smbclient -L windowsbox -U username
and it prompts you for the password.
Mount the share:
mount -t smbfs -o username=john //winbox/share /mnt
and it prompts you for the password.
Notes:
1) It’s OK to use domain users in both cases ("domainusername"). You need to use quotes to escape the backslash.
2) You can give the password in the commandline options list like this:
-o username="domainusername",password=topsecret
Note that this syntax saves the password. Also, it will be visible in the processes list.
3) The -t smbfs option can usually be omitted. The mount command should detect the type automatically.
