Actually that page is on specifically loading drivers using the Add From System option, as it states just above the line you quoted:
because most Windows workstations have an extensive list of printer drivers available on the system, the simplest way to add drivers for a Windows workstation is to upload them directly.
in in step 21 it says:
You can add drivers from the system only for the workstation type you are running.
and again if you go down to step 22 in the instructions.
This is from teh iManager built in help:
Driver Store Print Drivers
Drivers Platform
Select the operating system to add/delete print drivers from the Current Drivers list.
Note
By default, your workstation operating system is selected. You can add the driver only from your workstation operating system.
Add from File
Adds a print driver to the list from an .inf or .ppd file that you obtain from the printer vendor. If there is more than one driver in the .inf file, select the drivers that you want to install.
Add from System
Add drivers from the workstation you are running iManager from. The drivers installed on your workstation are made available for upload to the driver store. You can upload drivers only for the same platform as the workstation.
For example, if you are running iManager from a Windows* 2000 workstation, you can add only Windows 2000 print drivers. To add a print driver for Windows XP, you would need to add the XP driver from a .inf file that you downloaded from the manufacturer or .cab file that you copied from the XP installation CD, or use iManager from a Windows XP workstation.
And from teh OES 2 documentation online:
To add printer resources to the Driver Store:
1.In Novell iManager, click iPrint > Manage Driver Store, then browse to and select the Driver Store you want.
2.Click Drivers, then select the client platform you want to work with.
3.Do one of the following:
•Click Add from File to add printer resources from a printer driver .inf file or PPD file.
Uploading a PPD file is supported on the Firefox browser (Linux only).
•Click Add from System to add drivers from the workstation you are running iManager from.
The drivers installed on your workstation are made available for upload to the Driver Store. You can upload only drivers for the same platform as the workstation.
4.Select the driver you want, then click OK.
5.Click OK to save your changes.
While there is no explicit statement that an Add From File can be from any OS, intended for any OS, there is a clear statement in both places that Add From System must be performed that way. The obvious inference is that Add From File should have the flexibility. I know from testing just now that you can in fact upload drivers for Linux, Mac, Windows NT 4, Windows 2000 and Windows XP all from Windows XP. The error message I get is ONLY when Vista or Windows 7 (32 or 64 bit) is selected.
Again, all this process does is add the driver files to the server - not install them - there is no technical reason this should not work that I am aware of.
