OpenOffice is not running on a Native N900 platform yet. Using of OpenOffice will drain battery real fast, because it is not optimising to use on a portable device. It uses a lot of RAM and CPU.

KOffice is a smaller version which designed to run on the ARM processor CPU and low Mhz CPU. It is more efficient to run and will not drain your battery. But KOffice is not yet released for the N900.