To present an alternative to the whole naming structure instead of just suggesting names. The Zend Framework and other libraries have a naming structure that corresponds with the file's position in the tree. Half-fictitious example:
Class name Is in
-----------------------------------------------------------
Zend_Auth /Zend/Auth.php
Zend_Auth_Adapter /Zend/Auth/Adapter.php
Zend_Auth_Helper /Zend/Auth/Helper.php
Zend_Auth_Adapter_HTTP /Zend/Auth/Adapter/HTTP.php
so the underscore is the directory separator, and the last element of the name is the PHP file's name.
The main reason for this is that it makes autoloading extremely easy, but it's also a nice way for ordering libraries by task. Also, when you see a class used somewhere in your code, you can always tell which file it is in which is a great plus.
In your current method, the problem I see is that "src" is a very unclear description of what that class actually does. Maybe a more telling name (like "tools" or "query") would be in order, or maybe the main user class and should just be named "user"?
Applying the abovementioned example to that structure could result in
Class name Is in
------------------------------------------------------------
MyAppname_User_Update /User/Update.php
MyAppname_User /User.php
Oh and, what @Charles says in his comment. You should absolutely not be developing for PHP 4 any more. It is a dead version, and is no longer supported.