Right... finally solved this, but it really isn't very intuitive setting a new printer on CUPSWeb!
The stumbling block is the screen where a whole load of gutenprint files are listed; ahh, I'm getting somewhere now, I thought; you feel you're supposed to choose something from this list to continue, but NO, you have to resist and just click on 'Add Printer', and this brings you to the next page, where at last there's a list of printer makes. Click on this and you get all the models of one make, and hey presto.
Printing is, however, very slow and hesitant compared with Windoze. Are there any tweaks I might make to settings to speed up this printer, or might it just be that the system is struggling with not much memory??
Thanks for everyone's help.