If you are a basic user of word processing and spreadsheets and want to save money, you may want to consider the following alternatives to purchasing Microsoft Office. Both are free, easy to use, and work with the common file types (doc, xls, ppt).
OpenOffice.org is a free application that offers similar features to Microsoft Office. You can run it in Windows and Linux and even from a USB drive. It is easy to install and use. You will probably want to change the default file format for saving your documents to the familiar Microsoft extensions for compatibility with other users. This will work for both basic and intermediate users.
Google Docs is a free online application that allows you to use a word processor and spreadsheet. It is web-based, so there is no software to install to your computer. However, you can use it offline with Google Gears. The key features include the ability to store files online, access them from any computer, and collaborate with others. You can choose to share a document or spreadsheet with a friend and collaborate in real-time. This will work for basic users and those who wish to collaborate with colleagues.