I am using the metadata class for one of my apps on appexchange. Link for the class is https://github.com/financialforcedev/apex-mdapi/blob/master/apex-mdapi/src/classes/MetadataService.cls But the app is not working in Professional edition but rather in all editions because professional does not support API token. I did generated a case in support and they have given me a SOAP Token/Client Id to use. This token if appended in SOAP header will allow the users to access the app in Professional org as well. Token is: 'Abc/Dtest/' and this is the support link: http://wiki.developerforce.com/page/How_to_use_clientid
But can someone tell me how to append this Client Id in the present MetadataService class in SOAP header and not the java or C# code like given in support link?