You have to add the user (along with smb password) on the samba server, not the client. The list of samba users and passwords is independent of the normal users and passwords.
On the laptop, use the command:
Code:
smbpasswd -a desktopuser
This will both add the user and let you enter the samba password for dektopuser.
If you run smbpasswd on the desktop, or modify smb.conf (if it even exists) on the desktop, it will have no effect. These settings only affect the server, not the client. Therefore, it will only affect samba shares on the desktop (shared to other computers). It has no effect on how the desktop connects to samba shares on other computers.