^
Several options to edit Office files on the N900
Paid Native Maemo: Documents To Go (Can edit Word and Excel, only can view Powerpoint)
Free Native Maemo: Abiword (Edit Word docs), Gnumerics (Edit Excel docs), Cannot edit Powerpoint yet.
Free Easy Debian app: Open Office (Yup, full fledged Open Office on your N900, can edit Word using Open Office Writer, Excel using Spreadsheet and Ppt using Impress.) The main prob? It is slow to initialize, as it was running in Easy Debian

Maybe there was some error above, feel free to correct me though