PHP and Firebird; to use them together, is a great idea. How feasible is that is a challenging question for a beginner though? Here you go a short explanation for the PHP4 as well as the PHP5. If you are running the debian or the ubuntu and also the PHP5, then you should be really be conversant in the trade.
The simplest method to add the firebird support is to just add the interbase module to the existing PHP installation. In the case of windows, it is just a matter of just unpacking the PHP. Zip folder. When you are done with it, just extract that PHP_INTERBASE.DLL extension. There is another approach to it as well. You could try choosing the option interbase package when you are installing the setup.exe installer. In the latter case, please keep in mind that, there is a possibility that the installer will also try and install the file old gds32.dll by default. It is from the interbase 6.0. You will have to delete this addition by manual means. Instead you are now going to add the firebird’s file of fbclient.dll. You will have to rename it as gds32.dll though. In the case of Linux operating system you will have to compile the interbase.so file module.
Sometimes chances are there that people will not be aware of the fact where the php.ini is located in the system. In such a case, you could actually try to create the small PHP script, which will call the PHP internal function PHPINFO (); now read the output. There is a possibility to use the same function in order to determine if the extension is loaded properly or not. In case of Linux distribution you might not be able to find the section with extensions at times. In such cases, you could choose to have the separate .ini files as well for the extensions. PHP and Firebird makes a great combination altogether.