Safe PHP form submission and Validating PHP_SELF

Hey

My site has recently been hacked however it was no where near completion I had only tested it. There is not as much security on forms that there could be simply because I'm less experianced to just add it in as I go along.

Time to learn!   So far from what I have found a form script will double in size just to add this security so I'm a bit cautious as to what I really need to do.

This example...
http://www.gfx-depot.com/forum/-php-server-php-self-validation-t-1636.html
Sounds solid however I cant find anything else about it online so do I really need to use this measure?

I'm also asking here for any resource to developing SAFE forms. Get lots of info in Google about it but I can help thinking I'm going to miss something out and its going to be hacked anyway!

Theres  stripslashes and preg_replace! Do I use BOTH or one of them and WHERE do I use each of them?

oh and theres $user = strip_tags(substr($_POST['user'],0,32));  

but if they are all such code methods and required for security why cant I find any forms which use them all?

Any advice will be giving points :)

thanks