To anyone who is interested here's the deal -
If you are sharing a printer on an XP machine the URI for your samba printer must look like this -
which you will think is obvious, but there are a couple of funnies in here.
1st as a long time windows user I'm used to \\cartman\epson being the same as \\100.100.10.1\epson, given that cartman=100.100.10.1. In windows if you type an ip address like that as part of a machine name its clever enough to twig that its an address not a name so don't bother trying to resolve it. But linux thinks 100.100.10.1 is a Netbios name - good job! So the server MUST go in as a name not an IP. As I have no DNS I just stuck an entry in the hosts file.
2nd, for XP the guest user does not appear to have access to the printer, which on reflection is fair enough, but it took me a while to work it out. I have used the user/pass of my default XP user, otherwise you have to add a new user and you get the annoying user selection screen on bootup.
Pretty newbie stuff I know but it might help someone else!