"require": {
    "jdurand/magentsoap": "dev-master"
},
"repositories": [{
    "type": "package",
    "package": {
        "name": "jdurand/magentsoap",
        "version": "dev-master",
        "source": {
            "url": "git://github.com/jdurand/magentsoap.git",
            "type": "git",
            "reference": "remotes/origin/master"
        }
    }
}],
"autoload": {
    "psr-0": {
        "MagentSOAP": "./vendor/jdurand/magentsoap/src/"
    }
}

./composer.phar update

<?php

//API initialization
$api  = \MagentSOAP\MagentSOAP::getInstance();

if($api->catalogProductCreate($attributes, $attribute_set, $type)->success()) {
	// Cool
} else if($api->duplicate()) {
    // The product we tried to create already exists... we'll update it then
    if($api->catalogProductUpdate($attributes)->success()) {
        // The product was updated
    } else {
        // Something went wrong while updating the product
        echo $api->error());
    }
 } else {
    // Something went wrong while creating the product
    echo $api->error());
}

$api->end();