We've posted before about using Google Docs, but sometimes you need a full word processor and a way to make PowerPoint-like presentations. For that, we're fans of OpenOffice.
Using OpenOffice you can open, edit and save Word documents just like you would with Microsoft Office. The only difference - you don't pay for the program. You can also create slideshows and presentations using OpenOffice Impress or manage spreadsheets using OpenOffice Calc (just like Excel).
Just download the program and go. Easy as that.