Microsoft Office Starter 2010 is a cut-down version of the package which displays ads, and only contains limited versions of Office and Excel. But by way of compensation you can use it free of charge and without a product key.
Setup is straightforward, with the tiny installer downloading and configuring all the necessary files for you. Once it's finished you'll find your Programs menu has a new "Microsoft Office Starter" group, with links to Excel and Word Starter 2010, as well as a few basic tools (Clip Organizer, Picture Manager and so on).
Launch Word Starter 2010 and, if you're familiar with the full package, you'll immediately notice that this version appears rather basic. It has fewer ribbon tabs, for instance (References, Review and View are all missing). The tabs that are on offer don't provide as many options: click Insert and there are no SmartArt, Bookmark, Cross Reference, Quick Parts or Equations sections. And as you use the program so you'll encounter other limitations: no table of contents feature in Word, for instance, and no PivotTables or password protection in Excel.
The programs also display ads next to your documents. These aren't too obtrusive, no distracting animations or anything like that, but the fact that a panel needs to be allocated to them at all means there's less space available to view your work.
Still, one interesting bonus here is the inclusion of Microsoft's "Office Starter To-Go Device Manager", which enables you to create a portable version of the suite which you can run on any convenient Vista or Windows 7 PC.
And, even cut down there's still more than enough functionality here for many people. So if you're looking for a capable free word processor and spreadsheet, and tools like OpenOffice.org and LibreOffice don't appeal, then Office Starter 2010 is well worth considering as an alternative.
Please note Office Starter 2010 will NOT work with Windows 8.