Auto-enter calcs in IWP

[jdu98a]

I'm am working on an online application. I have the customers billing information set as a set of auto-enter calculation fields that auto fill with the data from the shipping information fields when the "same_address" field (contains a checkbox value: "same as shipping") is checked. Everything works fine from within Filemaker, but when accessing the page from the web the whole action is finiky at best. How can I get this function working for IWP?