Best word processor for Nokia N810 ?
Right now, it's Abiword in Easy Debian.
A maemo port of Abiword is being done, but not very stable.
Open office is simply very very slow in the tablet. (it takes about 90 seconds just to start)

Search the forum how to install Easy debian, it should not be hard.
Then install abiword("apt-get install abiword"), create a shortcut ("debbie abiword"), and enjoy.

Otherwise, for plain text, I recommend leafpad, simple and easy