It works!!!
Yesterday I thought I'd stuffed something because I couldn't even get zen cart 1.5 to work, let alone the template and stock by attributes etc - but eventually I contacted hostgator support and apparently they had to change the permissions or something, so they've now fixed it all up :)

AND better still - put in a test product and sizes etc today... and it worked!

THANKYOUSOMUCH for your help and for updating that add on in the first place - you're a legend