app/design/frontend/default/yourtheme/layout -> catalog.xml in section you need add:
<action method="addTab" translate="title" module="catalog"><alias>Mymodule="catalog">
<alias>My New Custom Tab</alias><title>>Myalias>
<title>My New Custom Tab</title><block>coretitle>
<block>core/template</block><template>catalogblock>
<template>catalog/product/mynewcustomtab.phtml</template><template>
</action>
in mynewcustomtab.phtml you can output you info
