<?php
$myServer = "localhost";//likely won't need to change
$myUser = "your_name";
$myPass = "your_password";
$myDB = "database_name"; 
$website_url = "http://mywebsite.com";

//connection to the database
$dbhandle = mssql_connect($myServer, $myUser, $myPass)
  or die("Couldn't connect to SQL Server on $myServer"); 

//select a database to work with
$selected = mssql_select_db($myDB, $dbhandle)
  or die("Couldn't open database $myDB");

//declare the SQL statement that will query the database


SET column1=value, column2=value2,...
WHERE some_column=some_value

$query = 'UPDATE wp_options';
$query .= 'SET option_value='.$website_url;
$query .= 'WHERE option_id = 1'; 
//can also use
//$query .= 'WHERE option_name = "siteurl"';

mssql_close($dbhandle);
?>