Sorry for not getting back to you sooner. I have realised the inventory implications of this...each variable will need an inventory level set, and that variable will need have a calculation done on that field in order to show current levels of inventory for the main product and each variable of that product. Eesh.
I'll need to run through the inventory example and work this out before I implement the AJAX menus on the product detail page, which could take me some time. :S
Be in touch as soon as I hit a wall! :|