How can I edit the default page for a new website? Where can I find it? and what files do I need to edit if I want to make this file a .php file?
You can do so at /root/ispconfig/isp/standard_index.html_[your_lang_here] You could make a php template, but you should modify a little bit /root/ispconfig/scripts/lib/config.lib.php search for things like this: Code: $mod->log->caselog("cp -fr /root/ispconfig/isp/standard_index.html_".$go_info["server"]["lang"]." ".$web_path."/web/index.html", $this->FILE, __LINE__);
Did you mean the default page for all new websites? That's the question Dan answered, but I read your question as a noob question of where to find the index.html file for the site and can it be a php. The noob answer is it's the index.html file in the "web" directory when you login as the user and just delete the index.html and upload an index.php for that to be the new default or home page for the domain.
Each reseller can specify a new standard index page for his clients. It's on the Options tab of each reseller in ISPConfig. And the admin can also specify a new standard index page for his clients under Management -> Server -> Settings.