To read and write from a text file, you may want to take a look at perldoc -f open. But you may want to take a look at DBI too. This way you can store and retrieve the info from a database. If you want to "encrypt" the passwords, you might want to peek at Digest::MD5.

If you've read that, and still have questions, please do post them (preferable with some of the code you use).