Since the Netra X! does not have an optical drive, you will need to do a temporary workaround:
Take the system and place it onto a workbench. Have access to a power source and to your console hookup.
Remove the top cover and find the IDE connectors on the systemboard.
Also find the molex power connectors from the PSU that can be used for drives.
Add a conventional PATA optical drive, jumpered properly so that the OBP sees it when you do a probe-ide.
Put a Solaris 8 or Solaris 9 disk into that optical drive.
Boot from that optical drive.
This link is to your Netra X1 as it was presented on the old Sun System Handbook. It's from a non-Oracle web site that mirrors that old discontinued resource.
This next link is to Oracle's documentation page for your system: