The N800 comes with the 'vi' editor. (You'll need to learn the 'vi' command set to use it. And it's essential to remember the 'escape' hardware button - see your N800 instructions leaflet). There's also an editor available from the menu system, I have never used it so I have no idea if it even edits pure text files, or what it does at all. Or you can always copy the file you want to edit to an SD card and edit it offline on your desktop computer.
-- Metalayer-crawler delenda est.
-- Current state: Fed up with everything MeeGo.