GPL means General Public Licence: Free.
I wouldn't bother patenting/licencing a script
unless it is very complex, if you put months and months of developing into it.
Why? because 99% of all scripts on the web are simple and do the same things.
If you try to licence a script that simply reads data from a form and emails it, you're just one of the many who have written such a script, and people will simply pass you by.
If you really want to protect your script, use the zend encoder thingy. But that also makes your script un-editable, so whoever "buys" your script will have to rely on you to make any required changes.
I'd definately go for GPL, and forget about making money.