To list shares on [server] visible to [username] use the following. You will be prompted for a password.
smbclient -L \\[server] -U [username]
To mount the //server/dir share on /mnt/dir, giving [username] and [password] as authentication:
smbmount //server/dir /mnt/dir -o username=[username],password=[password]
Alternatively, the same can be achieved using mount as a wrapper command:
mount -t smbfs //server/dir /mnt/dir -o username=[username],password=[password]
You can add the following to /etc/fstab so that you can mount the share with the command mount /mnt/share. This often means that the share will be mounted on boot by the /etc/rc.d/init.d/netfs script.
//server/share /mnt/share smbfs username=username,password=password 0 0