Can you use ddr2 memory in a ddr notebook for instance can you use a memory stick from a MacBook Pro in a powerbook g4?

If you insert a DDR2 memory card into a slot that usually holds a DDR memory card, the card will not be recognized by the system and a message will appear stating that there is an error with the memory card. Please do not insert memory cards into non-matching slots, you may damage the system. If your system does not become damaged as a result of poor memory card reading, your DDR2 card will simply only act as a DDR card and not make full use of the DDR2 capabilities.