Open Office is a wonderful set of programs, very similar to Microsoft Office Suite. It's got a word processor, spreadsheet & presentation program. Takes a bit of getting used to if you're coming from Word, but has most of the same features.
If you want something tiny,
Abiword is less than 15mb installed; the features are limited but it's got the basics covered. And there's a
portable version that will run off a USB drive instead of having to install it on someone else's computer.
OpenOffice also has a
portable version. (93mb download; 230mb installed.)