You could use something like this;

<form action="<?php $_SERVER['PHP_SELF']; ?>" method="POST">
<select name="employee_name">
<option value="Employee 1">Employee 1</option>
<option value="Employee 2">Employee 2</option>
<option value="Employee 3">Employee 3</option>
</select>
</FORM

<?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 '<input name="employee_name" type="text" value="'.$row['employee_name'].'"/>';
?>

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!