Hi, you can get the currently selected list index with "select_element.selectedIndex" or the value with "select_element.value"
Or you can get the text of the select option using:
Assuming the option just contains text.
I put up examples of these three approachs which you test try out here:
Click the buttons in the example to show the selected property and display the button's code in another box so you can see its onclick event.
The select element can be accessed as document.forms["addtobasket"].elements["sizechoice"] or by giving it an ID property (see above link for an example of the latter).
Look up "onsubmit" to find out how to cancel a form submission when necesssary (from memory I think you just return false).