Microsoft is giving you an opportunity to use and try out Office 2007 FREE for 2 months.
A Trial version allows you to evaluate the 2007 Office release for a limited amount of time, typically 60 days. In order to start your trial period, you must activate the trial software. Also, note that an internet connection is required to activate your trial.
You can convert from the trial software to a full-version either before or after your trial period ends, by entering a 25 character Trial or a Full product license key.
Free Alternative: OpenOffice.org 3.0