Funny you should ask this, with me having been through the PHP wringer recently! LOL.
Firstly, all PHP mail forms hide the address. There is an extra bit of code that is needed to bring up your form.html page if anyone tries to guess the address of your PHP form. There is also some code that will prevent your form being used to send spam mail. click here
Sites that I used, apart from this one obviously, include click here and click here
I'll post a copy of my code in a mo so that you can see what's what.