Example of Adding Data to an ExactTarget Data Extension via the SOAP API - API Starter Kit can be found here - http://docs.code.exacttarget.com/@api/deki/files/199/=PHP_APIstarterKit-V1.zip

add_data_to_de.php

<?
public function dataExtensionAdd($ExternalKey = '', $client = '') {

        try {
            /* Create the Soap Client */
            $soap = new EBG_ExactTarget_Client($this->wsdl, array('trace'=>1));

            /* Set username and password here */
            $soap->username = $this->username;
            $soap->password = $this->password;

            $DE = new ExactTarget_DataExtensionObject();
            //$DE->CustomerKey=$ExternalKey;                //Same as external key in user interface
            $DE->Name = 'NYDC Newsletter Subscriber Profile Data';
            
            // create clientid based on MID
            $clientID = new ExactTarget_ClientID();
            $clientID->ID = $client;
            $DE->Client = $clientID;

            $apiProperty1 =new ExactTarget_APIProperty();
            $apiProperty1->Name="subscriberkey";
            $apiProperty1->Value="[email protected]";

            $apiProperty2 =new ExactTarget_APIProperty();
            $apiProperty2->Name="EmailAddress";
            $apiProperty2->Value="[email protected]";

            $apiProperty3 =new ExactTarget_APIProperty();
            $apiProperty3->Name="FirstName";
            $apiProperty3->Value="Bob";
       
            $apiProperty4 =new  ExactTarget_APIProperty();     
            $apiProperty4->Name="Salutation";
            $apiProperty4->Value="Mr";
     
            $DE->Properties=array($apiProperty1,$apiProperty2,$apiProperty3,$apiProperty4);
            
            $Keys = new ExactTarget_APIProperty();     
            $Keys->Name = "Email";
            $Keys->Value = '[email protected]';
            $DE->Keys = array($Keys);
            
            $deoSaveOption = new SoapVar($DE, SOAP_ENC_OBJECT, 'DataExtensionObject', "http://exacttarget.com/wsdl/partnerAPI");

            $updateOptions = new ExactTarget_UpdateOptions();
            $updateOptions->SaveOptions = array();
            
            /*% ExactTarget_SaveOption */ 
            $saveOption = new ExactTarget_SaveOption();                
            $saveOption->PropertyName="DataExtensionObject";
            $saveOption->SaveAction=ExactTarget_SaveAction::UpdateAdd;

            $updateOptions->SaveOptions[] = $saveOption;
            $updateOptionsSaveOptions = new SoapVar($updateOptions, SOAP_ENC_OBJECT, 'UpdateOptions', "http://exacttarget.com/wsdl/partnerAPI");
            
            // Apply options and object to request
            $request = new ExactTarget_UpdateRequest();
            $request->Options = $updateOptionsSaveOptions;
            $request->Objects = array($deoSaveOption);
            $results = $soap->Update($request);
                                    
            return $results;

         } catch (SoapFault $e) {
            /* output the resulting SoapFault upon an error */
            //var_dump($e);
         }        
    }
    ?>

On line #12 a CustomerKey must be used in order to interact w/ the Data Extensions