Here is what we did:
1. Search the net for orca.msi and download it. (There is an alternative called InstEd)
2. Install it on your PC. Don’t worry, it even works on Windows 2000 J
3. Find the .msi-File (in our case it was BusinessObjectsClient.msi)
4. Right click it and select “Edit with Orca”
5. In the left pane find the entry „LaunchCondition“ and click it.
6. When done, select “( (VersionNT = 501 AND …” in the right pane, right-click it and drop the row.
7. Save the file, exit Orca and try to install again.
Please note: I installed and worked with parts of it: Desktop Intelligence, Designer, Rich Client. It worked as far as I can say by now. But I can’t guarantee for any errors or losses of data! Have fun anyway! J