Since your free trial was for an old version of Office, go ahead and uninstall it. Then you can download genuine, not pirated Microsoft Office 2010 beta for free. You can enjoy using the beta until October 2010. Microsoft Office 2010 goes on sale in June:
http://officebeta.microsoft.com/
Free on-line versions of Microsoft Word, Excel and PowerPoint are available from the same link. Click the Try Office Web Apps link for instructions. There's nothing to install. You use the free Skydrive versions of Microsoft Office from any computer - Mac, PC, or even LINUX - in your FireFox, Safari or IE web browser. These free Word, Excel, and PowerPoint versions don't expire. You can print and save your files to your computer even though you're using your web browser.
The URL below has links to many free products that compete against Microsoft Office, including open source OxygenOffice and NeoOffice (both of these are better than OpenOffice), Google docs, AppleWorks and others. Be real. Compatibility of the alternatives with Microsoft Office can be pretty bad if you do more than just simple stuff. None of the alternatives offer VBA add-in support, for example.
http://www.agentjim.com/MVP/PowerPoint/PowerPointForFree.html