Help With Connection

Im new at this and I am trying to connect to an mssql dtabase without any luck. I am using the following code;

$ref = $HTTP_POST_VARS["ref"];
$email = $HTTP_POST_VARS["email"];

$db = mssql_connect("server", "user","password");
mssql_select_db("table",$db);

$query = "SELECT * FROM HEALTH WHERE compno = '";
$query .= $ref;
$query .= "'";
$query .= " AND callname = '";
$query .= $email;
$query .="'";
$result = mssql_query ($query);
$count_rows = mssql_num_rows($result);

while ($row = mssql_fetch_array ($result))
{
$ref = $row['compno'];
$desc = $row['catdisplay'];
$details = $row['catdetails'];
$complaint = $row['complaint1'];
}

if ($count_rows > "0")
{
?>
<?php echo $ref; ?>

I keep being given the "Call to undefined function: mssql_connect()" error. I have changed the ini file on the server but seems to have given me no luck.

Can anyone help???