Okay I have this MySQL database form and am trying to add validation to it. After 2 days of fighting with it, I thought I would get some advice. Would like that the selected item from dropdown and Firstname, Phone, Email, are all required. Then I want to verify that the data in the Firstname, Lastname, Phone (doesn't have to be any special format), Email and Comments are all acceptable formats before putting in database. Here is what I have so far:

 <?php 
include('inc_header.php');
if(isset($_POST['add']))
 {
 require('dbcon.php');
 if(! get_magic_quotes_gpc() )
{
$Id = addslashes ($_POST['Id']);
$List = addslashes ($_POST['List']);
$Firstname = addslashes ($_POST['Firstname']);
$Lastname = addslashes ($_POST['Lastname']);
$Phone = addslashes ($_POST['Phone']);
$Email= addslashes ($_POST['Email']);
$Calltime = addslashes ($_POST['Calltime']);
$Comment = addslashes ($_POST['Comment']);

}
else
{
$Id = $_POST['Id'];
$Date = $_POST['Date'];
$List = $_POST['List'];
$Firstname = $_POST['Firstname'];
$Lastname = $_POST['Lastname'];
$Phone = $_POST['Phone'];
$Email = $_POST['Email'];
$Calltime = $_POST['Calltime'];
$Comment = $_POST['Comment'];
 }

 $error = '';

 //put chosen function here
  function validate_Firstname($input, $pattern = "/([A-Za-z0-9])")
 {
    return !preg_match($pattern, $input);
   }

  function validate_Phone($input, $pattern = "/([A-Za-z0-9])")
 {
    return !preg_match($pattern, $input);
  }
 function isValidEmail( $Email ){
    return filter_var( $Email, FILTER_VALIDATE_EMAIL );
 }

  //get values and validate each one as required
  $List = mysql_real_escape_string($_POST['List']);
     if(!$List){ $error .= "Please choose one<br />"; }

  $Firstname = mysql_real_escape_string($_POST['Firstname']);
    if(!$Firstname){ $error .= "First name is required<br />"; }

//get values and validate each one as required
  $Lastname = mysql_real_escape_string($_POST['Lastname']);
    if(!$Lastname){ $error .= "Last name is required<br />"; }

  //repeat for each field
  $Email = mysql_real_escape_string($_POST['Email']);
    if(!isValidEmail($Email)){ $error .= "The email entered is invalid<br />"; }

  //and so on...

  if(!$error){
     //add insert into database code here

 $sql = "INSERT INTO contacts ".
   "(`Id`,`Date`,`List`,`Firstname`,`Lastname`,`Phone`,`Email`,`Calltime`,`Comment`)".
 "VALUES'$Id,','$Date','$List','$Firstname','$Lastname','$Phone','$Email','$Calltime','$Comment')     ";
 mysql_select_db('hmintcwa_contacts');
 $retval = mysql_query( $sql, $conn );
 if(! $retval )
 {
  die('Could not enter data: ' . mysql_error());
 }
 echo "Entered data successfully<br /><br /><a href=contactsadd.php><font       color=#000000>Back</font></a>\n";
 mysql_close($conn);
}
else
 {

 ?>

 <form method="post" action="<?php echo htmlspecialchars($_SERVER["PHP_SELF"]);?>" name="ContactForm">
 <table bgcolor="#000000" width="500" cellpadding="5" cellspacing="1" border="0">
 <input type="hidden" name="Id" id="Id">
 <tr>
 <td bgcolor="#e9e9e9" align="right">Requested Info</td>
 <td bgcolor="#ffffff" align="left"><select name="List">
 <option value="0" > Please Choose One </option>
 <option value="Market Analysis" > Market Analysis </option>
 <option value="Consultation" > Consultation </option></select></td></tr>
  <tr>
 <td bgcolor="#e9e9e9" align="right">Date</td>
 <input name="Date" type="hidden" id="Date" value="<? print(Date("l F d, Y")); ?>" />
<td bgcolor="#ffffff" align="left"><? print(Date("l F d, Y")); ?></td>
</tr>
 <tr>
 <td bgcolor="#e9e9e9" align="right">Firstname</td>
 <td bgcolor="#ffffff" align="left"><input name="Firstname" type="text" size="20" id="Firstname"></td></tr>
 <tr>
 <td bgcolor="#e9e9e9" align="right">Lastname</td>
 <td bgcolor="#ffffff" align="left"><input type="text" name="Lastname"  size="20" id="Lastname"></td>
 </tr>
 <tr>
 <td bgcolor="#e9e9e9" align="right">Phone</td>
 <td bgcolor="#ffffff" align="left"><input type="text" name="Phone" size="20" id="Phone"></td></tr>
 <tr>
<td bgcolor="#e9e9e9" align="right">Email</td>
 <td bgcolor="#ffffff" align="left"><input type="text" name="Email"  size="20" id="Email"></td></tr>
 <tr>
 <td bgcolor="#e9e9e9" align="right">Preferred Calltime</td>
 <td bgcolor="#ffffff" align="left"><input type="text" name="Calltime"  size="20" id="Calltime">  &nbsp;&nbsp; If none put N/A</td></tr>
 <tr>
 <td bgcolor="#e9e9e9" align="right">Comment</td>
 <td bgcolor="#ffffff" align="left"><textarea name="Comment" cols="40" rows="8" id="Comment"></textarea></td></tr>
 <tr>
 <td bgcolor="#e9e9e9" align="right">&nbsp;</td>
 <td bgcolor="#ffffff" align="center"><br>
 <input name="add" type="submit" id="add" value="Add Contact"><input type="reset" name="Reset" value="Clear Form"><input type=button value="Cancel" onClick="history.go(-1)"><br>&nbsp;
 </td>
 </tr>
 </table>
 </form>
 <br>&nbsp;</center>
 <?php
 }
  ?>
   </body>
       </html>

So far I just keep chasing error message. Please forgive formatting I am trying to learn be gentle.