Powerpoint,Excel,Word. Product key ?

Have you tried asking in the Microsoft forums?
http://www.officeformac.com/productforums/

Sounds like Office came as a trial package and now you need to purchase it. If you don't have separate disks for MS Office with that info then you don't have a legitimate copy of Office.

Please find below the official Microsoft blurb relating to this issue:

'If your copy of Office 2008 was installed with an invalid product key, or if you mistakenly used the same product key to install Office 2008 on more than one computer, you must remove the invalid product key and enter a valid product key to use Office 2008.

1/ In the Finder, select /Applications/Microsoft Office 2008/Office/OfficePID.plist, and move it to the Trash.

2/ Select /Users/<username>/Library/Preferences/Microsoft/Office 2008/Microsoft Office 2008 settings.plist, and move it to the Trash.

3/ Restart.

4/ After your computer restarts, open any Office 2008 application. The Office Setup Assistant opens.

5/ Accept the software license agreement, and then enter your valid product key. The product key is located on the back of the Office 2008 for Mac DVD sleeve or on the back of the Install Guide.'

You will need to find your original product key/serial number before you can get it up and running again.

In the short term if you can't find it you can use OpenOffice It won't give you an alternative to Entourage but at least you will be able to open and work on existing Microsoft Office documents. If you create docs from scratch and are sending them to other people either in OpenOffice Menu/Preferences under Save set the docs to save in Windows XP etc format or Save As when saving your docs so that the recipient can open them in their copy of Word, Excel etc