Just to be absolutely clear, you will get Silver status within a few business days of flying your 30th segment and that will be valid through Feb 2007. This is because you qualified in the 2006 program year and it will recognize you through the end of the 2006 benefits period (which lasts through Feb 2007). You will be mailed a 2006 Silver Elite card and Benefits Guide within a few weeks. Starting sometime in February 2007, your profile on NWA.com will reflect your status as Silver through February 2008 and near the end of February/early March, you will receive your 2007 Silver Elite card and Benefits Guide.
This is always a confusing topic for some reason, don't worry.