These days there’s no reason to buy Microsoft Office.
The Open Office Organisation provide a fully featured, open source, office suite completely free of charge which is completely compatible with MS Office.
You can download Open Office at http://download.openoffice.org/
If you don’t want to download Open Office or if you’re working on a different computer, as long as you have an internet connection, you can use Google Docs.
You need a Google Mail account but as long as you have you can use Google Docs completely free and again it’s compatible with MS Office.
You can find Google Docs at http://docs.google.com