cgiemail -form question

[Patricia]

I made a form that is working... Now the client wants the form to update the
content of the fields as the user fills out the form. For example, if they
pick 2 t-shirts in a certain field (that cost 10 each), then in the
subtotals field for t-shirts, it already shows up the value for 2 t-shirts,
$20...

Is this possible with a form in a html that submits the info through
cgiemail? Do you know where I can get a code that would make this happen?

Thanks!
Patricia