Hi. the California Service Center, where your I-539 would be pending if you live in Illinois, is currently processing I-539 Applications filed on April 16, 2008. Click on the USCIS link below to view processing times.
To change your status from H-1B to F-1 an I-539 - Application to Extend/Change Nonimmigrant Status would have to be filed. Check with your school's International Student Advisor as your school may be able to assist you with the filing.