PHP Email Script Modification

Description

I have a PHP script which runs on a static HTML site that is used to send out emails (see attached).
I'd like 2 changes made to it:
1. I'd like the email sent to me to be in HTML format not plain text. I have all the HTML code for the email I just need the behaviour changed and somewhere to paste the code.
2. I'd like a receipt/auto-response sent out to anyone filling in the form (again in HTML). I can add all the code for the email I just need things re-configured to allow this.
Any questions please let me know.