Note that since this is the trial version of Office Professional, not only do you get Word, Excel and PowerPoint, you also get Publisher and Access, two other very nice tools, and a few other tools. For free, it's definitely worth a try.
If you were interested in simply purchasing it, there is a "Home and Student" version, which is designed for home users that will be doing common school related tasks. The "Home and Student" version includes Word, Excel, and PowerPoint. This is much cheaper than the standard versions of Office, with a retail price of $150.
At this point, it is a little over $100 to purchase it on Amazon. I'll link to that below.
- Office 2007 Home and Student version on Amazon (PC Version)
- Link to free trial download page
(Note that even though this is not from "Microsoft.com", it is what Microsoft links you to. I checked)