Force SCCM client to check advertisements

System ManagementCustomize SMS Using Local Policies
http://technet.microsoft.com/en-us/magazine/2006.09.customizesms.aspx

Force Task Sequence Execution without Advertisement
http://social.technet.microsoft.com/Forums/en-US/configmgrsdk/thread/298b32f6-746c-473a-b7ce-6bb51cfe1270/

Force SCCM Client to Check for New Advertisements
http://social.technet.microsoft.com/Forums/en-US/configmgrswdist/thread/a1066dfb-a71e-4e52-b7b7-c225ea0935a4/