php mail problems

I've got a basic php mail script on my site that I'm having a few problems with.

The script sends me the content of a submitted contact form using the mail() function and it works very well, but a while ago it started sending me emails with all blank fields, which didn't worry me to much.

Recently though I've been getting emails from it that contain an email address in every field. The addresses are random digits @ mydomain.com [EG. kjhdkjh@mydomain.com] even in the IP and browser information fields.

Now I presume someone is trying to use the script to send spam, and I guess it's reasonably simple to stop but I'm reaching the limits of my php knowledge here so I'm hoping that one of you guys could point me in the right direction.

My URL is http://sounds-alarming.co.uk

Same thing here..

http://www.sitepoint.com/forums/showthread.php?t=299286

what you need is a validating script, you know with the numbers at the bottom ensuring that a human is filling out your form.
go to hotscripts.com in the php section im sure there is somehting there, also dreamweaver if you have it has a button under application or something that can check to make sure everything is legit.

you definately need to have a good look at your script, the last thing you want is for spammers to be able to add extra headers into the script and use it to send spam:
http://securephp.damonkohler.com/ind...mail_Injection

This article has some interesting stuff about it