Text File on Server

Im trying to keep a text file of accounts, passwords, etc on a webserver. I want to make a script that lets people make new accounts entering data for account name, pass, email and it wont make accounts if certain conditions are met. Like the email @hotmail.com is used it wont make the account.

Any one have a script like this? Preferably PHP

Text file????

This sort of use, allowing users to access, and update the data would be better suited to XML. I know how to do it in ASP & ASP.NET but not PHP.