MySQL is working happily on many of our machines (mostly Windows XP and 2000) so that's free and found with google.com I'll stop writing about MySQL here.
As to PHP you'll want to use what version they used and http://www.en.wampserver.com/ looks real interesting.
Bob
Hi guys,
Could anyone recommend some free software so that I can set up a local server using PHP and MySQL. I need to test a website - the developers are adamant that it works fine on their local server, but we have some persistent bugs when we upload it to our webserver. After a week spent making no progress, I have decided to set up a local server myself to test the site and see if the problems are server-side or design-side.

Chowhound
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