If you do not own Microsoft Office or any of the programs (Word, Excel, etc.), you can still read documents using Microsoft's free reader software.
Here's how:
Google offers Google Pack (http://pack.google.com/) which contains, among other things, StarOffice from SUN Microsystems.

Note that this user has already installed the Google Toolbar for IE, Picasa, etc. On the same screen below, you can read detailed descriptions about the software in Google Pack.
To get the software, uncheck the software you do NOT want to install and check the box for the software you want to install -- for example StarOffice -- and click the Install Software button. Follow the prompts and Google Pack will be installed on your computer and StarOffice will be downloaded and installed.
When complete, you will have the premier Office competitor on your computer. It will open, read, and save all Microsoft Office documents.
Google Pack will let you know when there is an update to StarOffice (and any other software you installed), so you will always have the latest versions.
Enjoy!