To access Salesforce via a desktop application or other API-based application, you must replace your current password with a combination of your password and a security token:

1 Log in to Salesforce via the browser to request your security token.

2 Go to Setup -> My Personal Information -> Reset Security Token.

3 Click the Reset Security Token button to trigger an email which will contain your security token.

4 Select and copy the token from the email.

5 In the application, replace your password with combination of the password and the security token. For example, if your password is "MyPassword" and your security token is "XXXXXX", you would enter "MyPasswordXXXXXX" into the password field.

The security token will be sent to your email address (assuming you're the admin).

Credit goes to this url for this post. I repost in case his site goes down and the info is lost. http://www.mikesimonds.com/adding-event-calendar-t111.html
The object to update or insert a new calendar event is the "Event" object in salesforce

There are 4 required fields that need to be inserted in order for the event to be added to your instance of Salesforce.

Assigned To
Subject
Start (date and time)
End (date and time)

Those API field names are

Owner Id
Subject
StartDateTime
EndDateTime

Remember that Salesforce times are all set to GMT, so you have to account for that. Since my time is set to -6 GMT, I have to adjust my code for that:

PHP Code:

<?php
ini_set("soap.wsdl_cache_enabled","0");


require_once ('./soapclient/SforcePartnerClient.php');
require_once ('./soapclient/SforceHeaderOptions.php');

$mystuff = array('OwnerId'          => '00550000000wI2LAAU', // Assigned To
                 'Subject'          => 'PHP Event Addidtion Test 2', //Subject
                 'StartDateTime'    => '2008-08-05T12:00:00.000Z', //Start time of event
                 'EndDateTime'      => '2008-08-05T13:00:00.000Z'); //End time of event **ALL TIMES ARE GMT, REMEMBER TO ACCOUNT FOR THIS****
//clean User to allow changing of characters to XML
$mystuff = array_map('htmlspecialchars',$mystuff);

//try to add User from from array
try
{
    //salesforce login and wsdl
    $wsdl = './soapclient/partner.wsdl.xml';
    $userName = "me@email.com"; // change this to a valid email
    $password = "password"; // change this to a valid password

    //connect to salesforce
    $client = new SforcePartnerClient();
    $client->createConnection($wsdl);
    $loginResult = $client->login($userName,$password);

    $sObject = new sObject();
    $sObject->type = 'Event';
    $sObject->fields = $mystuff;


    //this part adds the contact to salesforce
    $result = $client->create(array($sObject));

    if ($result->success)
    {
        echo "A new Calendar event has been added to your instance of Salesforce with an Id of ".$result->id."<br />";
        echo "**************** ALL DONE ****************<br />";
        exit;
    }
    else
    {
        $errMessage = $result->errors->message;
        echo $errMessage;
    }

}
catch (exception $e)
{
    // This is reached if there is a major problem in the data or with
    // the salesforce.com connection. Normal data errors are caught by
    // salesforce.com
    echo '<pre>'.print_r($e,true).'</pre>';
    return false;
    exit;
}
?>