MacCentral readers were first to receive information two days ago about Apple's intention to allow existing Titanium PowerBook owners to upgrade their system with a combo drive. Few details were available at the time, but today Apple released more information on the subject. Apple will offer The PowerBook G4 Combo Upgrade Program from January 14 - March 30, 2002, for owners of a 550MHz or 667MHz PowerBook. Owners of earlier PowerBook 400MHz and 500MHz models are not eligible for the upgrade program because the combo drive will not fit, according to Apple. Apple will post a phone number on its Web site January 14 for customers to call and place an order. When calling to place your order have the serial number of your PowerBook available -- the Apple representative will verify that your system is eligible for the upgrade program. You will also be asked for your shipping address and credit card information. When your drive comes in, you will be sent a shipping box so you can send your PowerBook to an Apple Repair Center -- your credit card will be billed once the upgrade is complete.