There are export restrictions on PowerBook computers. You should contact the local U.S. Customs Department to find out what paperwork you'll need to export and import the equipment. If the value of the equipment is over $2500, you also need to contact the local Department of Commerce and obtain a Shipper's Invoice.
You should not check the unit with luggage. If you must check it, use the original box. To avoid damage while travelling, a well padded and durable case should be used to transport the PowerBook. Be sure the battery is charged to demonstrate that the unit is functional.
Apple has a global warranty so that products purchased in or out of the United States can be repaired at any Apple authorized service provider. Be aware that parts availability may be limited and as a consequence, repair times may be extended while out of the country of original purchase. Be sure to have your proof of purchase with you when travelling overseas to validate warranty coverage.