OK, a bunch of things I'll suggest:
1. Are the Samba daemons running at the time that you're trying to add the printers? Neither of you with the problem has named your distribution, and all distributions do not necessarily set up Samba to run at boot without the user intervening. The Samba daemons are called smbd and nmbd, and are likely found in /usr/sbin (you can do a whereis smbd/nmbd to find or confirm their exact location). You can run the 'top' command in a terminal to see if they are running, or use the System Monitor of your DE to see the currently running processes. If not, you should start the daemons by opening a terminal, using the 'su' command to switch to a root terminal, and then run the daemons. If everything else is properly configured, the printer may now be able to be added and work properly. If you've had to start them manually, check your distribution's documentation for how to add them to the default runlevel so they start automatically.
2. Stupid question, but you both are trying to add these printers as root, right? Only root has the right to manage hardware.
1. Look at /etc/samba/smb.conf. Is the workgroup/domain set to the same as the Windows workgroup/domain that shares the printer?
The default Samba workgroup is usually wrong, and if it is, you won't be able to connect to the printer, as you are not a member of the authorized group to use it.
2. In my experience (HP printer directly connected to a Win2K
machine via a workgroup and not a domain), the only command that successfully adds the printer in a working state is smb://username:password@ip_of_the_windows_box_(but you can maybe use the hostname instead)/share_name_of_the_printer
There are a couple of caveats with this command; the user/pass must be known to the Windows box
(meaning the user must be added to the list of known users by the Windows Administrator), and the user must have administrative privileges on that box.
Otherwise, apparently CUPS won't have access to some file that it needs to add the printer. This may also be a fluke of my particular printer or setup with Win2K; certainly this is not an issue with Win98 (which doesn't even have administrative rights), and it may be possible to work around this with a finer-grained user security policy (or by having an "extra" box used exclusively as a print server, which wouldn't have anything that might be in danger of being hacked in the first place).
If necessary, it's very unfortunate, though, as the "smb:\\blah_blah_blah" command is sent in cleartext. But there seems to be nothing to be done except to make a junk admin who doesn't have access to any other shared files on the network, and to make sure your firewall is protecting you from unauthorized outside access so that this data won't get hacked.
3. As for the "lpadmin: add-printer (set model) failed: client-error-not-found" error that a1flecke and bbo report, this Samba+CUPS HOW-TO
(which both a1flecke and bbo should read, it seems quite comprehensive) indicates that:
If you received "error: client-not-possible" then chances are there is a typo
in your URI, or your link to smbspool is missing or pointing to the wrong place.
So that's pretty clear. I think that whatever is not covered by my post is covered by the document linked above, so I hope that this information helps to solve the problems that both of you are encountering. Good luck.