Need help with contact form (required fields)

I used the kirupa tutorial to create my form but there are a couple of more types of fields I need…

  1. On my contact form I have some text fields I would like to make required before the message is sent to my email address so Everything is filled out. How do I do this?

  2. I Have check boxes I would like to put a field next to, but I want the field to be disabled unless the checkbox is checked. How is this done?