Windows 2003 XP search file content does not work...

Solution:
Most administrators have been doing this for years on Windows 2000. The "search content" behavior changed in 2003 (XP is similar). Basically Microsoft added options be enabling specialized filters to perform the search. For example the HTML filter skips the comments.
To add the plain text filter to files with the .php extension add the following to the registry:
HKEY_CLASSES_ROOT\.php\PersistentHandler\(Default) = {5e941d80-bf96-11cd-b579-08002b30bfeb}
Take a look at:
HKEY_CLASSES_ROOT\.htm\PersistentHandler the HTML filter is {eec97550-47a9-11cf-b952-00aa0051fe20}.
The .htm files are searched with the filter {eec97550-47a9-11cf-b952-00aa0051fe20}. PHP.net could provide Windows users with a special search filter. It's a good design, but not very easy/modular to configure. Imagine the average Joe modifying his registry to add a search filter for different basic file types...scary...

Many file types do not have a filter defined by default and adding a filter to all file types might be a little time consuming and a constant activity.
The other solution is to enable the search of all file type (ala Windows 2000 Server).

For this open the MMC of Index Server, right click your "Indexing Service" entry and select "Properties" and check the option "Index files with unknown extensions".
Voila!

Ref:
http://support.microsoft.com/default.aspx?scid=KB;EN-US;309173
http://support.microsoft.com/kb/309173/EN-US/