STUARTY I have just encountered the same problem. However I managed a workaround to get the problem resolved.
I have a colleague who had his LabelWriter 330 Turbo working on his 10.4.8 OSX - he didn't have any trouble. So I got a copy of his driver from his users/library/printers folder. I copied this to my users/library/printers folder. Now when I select the Dymo labelwriter from the list it adds the printer and it works just like before. If you need a copy of the driver then let me know your e-mail.
(Version 7.6)