Form Browser / Form Builder - optional fields...?

[numer9]

Hey,
i'm working on a project and I have a question, maybe you'll give me some suggestions...

I'm creating a big form. It has many different fields, and Form Builder with Form Browser work great. But I need one more thing and i can't find it. It's optional fields. That is: there's a field 1, with radio button option "true" and "false". If you choose "true" fields 2 and 3 should stay enabled; if you choose "false" - it should be disabled. Can it be done in these modules? If not - any suggestions, how to start programming this feature?

and second thing is javascript operation field. I got fields 1, 2 and 3 with numeric values. I need field 4 with dynamic (javascript) sum of 1+2+3. Any hints?

big thanks!