I searched a couple of days and didn't find how can i put my custom fields in standard SalesForce object (Account, Lead, Opportunity etc...). I found only info about metadata API described here, but it explains inserting new metadata only on custom objets. I found this code too, but it works only for custom objects too. Does anybody knows more about this stuff? Thanks.
EDIT: Here is final working code for those who can't find example.
// SOAP_CLIENT_BASEDIR - folder that contains the PHP Toolkit and your WSDL
// $USERNAME - variable that contains your Salesforce.com username (must be in the form of an email)
// $PASSWORD - variable that contains your Salesforce.com password
define("SOAP_CLIENT_BASEDIR", "../../soapclient");
require_once (SOAP_CLIENT_BASEDIR.'/SforcePartnerClient.php');
require_once (SOAP_CLIENT_BASEDIR.'/SforceMetadataClient.php');
require_once ('../userAuth.php');
try {
$mySforceConnection = new SforcePartnerClient();
$mySoapClient = $mySforceConnection->createConnection(SOAP_CLIENT_BASEDIR.'/partner.wsdl.xml');
$loginResult = $mySforceConnection->login($USERNAME, $PASSWORD);
$myMetadataConnection = new SforceMetadataClient(SOAP_CLIENT_BASEDIR.'/metadata.wsdl.xml', $loginResult, $mySforceConnection);
$customField = new SforceCustomField();
$customField->setFullName('Account.MyCustomFieldb__c');
$customField->setDescription('Description of New Field');
$customField->setLabel('My Custom Field Label');
$customField->setType('Text');
$customField->setLength(255);
print_r($myMetadataConnection->create($customField));
} catch (Exception $e) {
echo $myMetadataConnection->getLastRequest();
echo $e->faultstring;
}