If you have installed Snow Leopard to a blank hard drive and elected not to install Rosetta (the software that allows PowerPC applications to run on Intel-based Macs - it is not selected by default on new installs unless you are upgrading), you may find that the Microsoft Office 2008 installer will not proceed without first prompting you to download and install Rosetta.
For those that upgraded from Tiger or Leopard, your existing Office 2008 installation will continue to run fine, but you should ensure that you have installed the latest Office updates, use the links below or run Microsoft AutoUpdate (launch an Office app and go to Help > Check for Updates).
To install Microsoft Office 2008 without Rosetta, try the following:
1. Download the following Office updates (you will need them later):
a. Download Microsoft Office 2008 for Mac Service Pack 1 (12.1.0) (180 MB)
b. Download Microsoft Office 2008 for Mac Service Pack 2 (12.2.0) (297 MB)
c. Download Microsoft Office 2008 for Mac 12.2.1 Update (24 MB)
2. Install Microsoft Office 2008 using Terminal (command line), enter the following command and your password when prompted:
Where /Volumes/Office\ 2008/Office\ Installer.mpkg is the path to your Office 2008 installation package. If you're not sure what the path is as it may differ from the above example, this will complete it for you:
sudo installer -package /Volumes/Office\ 2008/Office\ Installer.mpkg -target /
Enter: sudo installer -package<space>, then drag Office Installer.mpkg from your Office 2008 CD or Disk Image to the Terminal window, and then type: -target /
3. After the installation has completed, close Terminal and install the Office Updates that you downloaded in step 1 as normal and in order, a, b, c.
That's it, you're done. Launch one of the Office 2008 applications.
So far I have not come across any issues with this.
If it turns out there is some component in Office 2008 that is PowerPC and fails to operate correctly, you will need to install Rosetta or wait for an update from Microsoft.