Pierre-Alain Joye has posted an example of one way to use the XDebug software - to debug the symfony framework or any other script (with the help of vim).
Xdebug is one of the best debugger and profiler for php (maybe the only good one in open source :). The only problem is its lack of dedicated client. The only problem is its lack of dedicated client, however there is many plugins for many IDE or editors like Eclipse PDT or weaverslave and even for my favourite editor, Vim.
He quickyl runs through the installation of XDebug in your installation and the script needed to set up the debugging in vim. All that's left is to add the "XDEBUG_SESSION_START=1" flag to the end of your script name and letting the information flow in.