"so am i right in understanding that if i added an "add to cart" button/form and dropped the drop-down list into this form, that will send the version to the cart?"
It will submit the information with the form... you could update the add to cart to set that information to a cart column you have created to hold it.
"so from there i would update the "add to cart" server behaviour to specify that it sends the version id info plus the vat value from the product recordset?"
The versionID would come from the list they selected in the submitted add to cart form... the vat value would come from the recordset. Once you add the columns to the cart object they will appear and you can set them in the add to cart server behavior.
You need to add the columns to the cart before updating the add to cart server behavior.
Once you have added the columns and calculations you can base your VAT tax on the total of the calculated AmountTaxed column using a tax rule on the tax tab.
