contact the Member Service Centre at goldpointsplus@carlson.com or call +44 207 949 0379 and mention the promotional code indicated in your XING promotion (Code: OPBCSL09).Now, Silver status doesn’t get you much.
But it does get you “Our World, Your Lounge” benefits in Europe, Middle East, and Africa: elite members are welcome any time in any hotel for a free coffee, tea or hot chocolate for two people and to use free wireless internet.
Judging from the Flyertalk discussion - a simple email to goldpointsplus (after you registered for goldpointsplus seperately here) will do the trick.
UPDATE - did the online registration - no need for email!