You could use something like this;
Employee 1Employee 2Employee 3<?php
$employee_selected=$_REQUEST['employee_name'];
$query="SELECT * FROM employees WHERE employee='$employee_selected'";
$result=mysql_query($query);
$row=mysql_fetch_array($result, MYSQL_ASSOC);
// THEN YOU NEED THE TEXT BOXES
echo '';
?>
This script will get the employee name from the drop down, search the database and display the details you require in the respective textboxes.
I have a Customer/Employee management system on my website you could purchase if your stuck! I can totally customise it for you!