Read this.

Windows® XP - Search Problems
http://www.dougknox.com/xp/tips/xp_bad_search.htm

Then get this.

xp_persisthandler.vbs - Enable XP's "Search" to find text in files.
© Doug Knox - rev 2/5/2002
http://www.dougknox.com/xp/scripts_desc/xp_fix_search.htm

More information here.
Windows XP - Search Problems
http://www.dougknox.com/xp/tips/xp_bad_search.htm

And more information here.
Using the "A word or phrase in the file" search criterion may not work
http://support.microsoft.com/kb/309173

{5e941d80-bf96-11cd-b579-08002b30bfeb} is the CLSID for the Plain Text
persistent handler.

This is a big drop off by MS, in that the find routine only seems to search
through known or 'approved' file types. If you want it to search through
rarer extension, then you need to use the xp_persisthandler via the link
below:-

http://www.dougknox.com/xp/utils/xp_filefilter.htm

When you run this script, give it the extension you want added to the
registry (in your case php) and the find operation should then work. I had
to do the same for ads and adb files for use with ADA programs. It works
fine after this is done.

A nuisance, I know, but I think MS wanted it this way to prevent looking in
files it did not want you to mess with - I presume!??

Hope this helps

Martin