I think that such a test will test server's load capabilities rather than the php code. So if you test the site with any software on your home webserver is one thing, but having it tested on the remote machine, where the site will be live and running is completely different story.
I rather recommend you check your code for vulnerability like sql injection, and validate your css and html on the w3c validator. This in my opinion is better than stress test for server capabilities!

@Rhyan

Thanks for your response back.....

Now the real point is that, I have to show it, as it is the requirement of client.

your points are valid that, go for Sql Injection, validation etc.... but here the scenario is different, So if anyone have an idea than kindly share it at this spot
Waiting....

Regards
scorpionz

What google is saying?

@jack239
Thanks for taking interest
unable to get a better treatment from google, I just wana know what particularly use for PHP Apache. and atleast open source...

if anyone have a knowledge, just share here, so Problem can be fix for many others as well.

Regards
scorpionz

Ok, google gave this links in top 10

http://www.smashingapps.com/2008/01/...-pressure.html

OR
http://www.dotcom-monitor.com/web-load-stress-test.asp
Hope these will be what you need.