Hi, Greg,
Here's something that might help:
Basically, these are the steps to manually remove the Windows installer data
for Office
(these were copied from a helpful Microsoft person, so they're pretty
explicit):
1. On the Start menu, click Run.
2. In the Open box, type "Regedit" (without the quotation marks) and then
click OK.
3. Locate and expand the following key in the registry:
HKEY_LOCAL_MACHINE\Software\Classes\Installer\Products
4. Below the \Products key, select each 32-character {GUID} until you find
the one whose ProductName value matches your version of Office.
5. With the 32-character {GUID} for your Office product selected, export
this entry for backup.
6. Then please delete the entry from your computer. Restart computer.
7. Then please insert the Office Installation CD to run Setup for Office
again to reinstall Office on the computer to the original folder on your
computer.
8. After installation, please check the issue again.
When you say you get an error message at about 50%, if you search for that
error message in the Knowledge Base, you might find some helpful
information. Posting that you "get an error message" doesn't really give
enough information for someone to help you troubleshoot.
Hopefully that will help.