Yes, you need magic :-)
normally the "9407-515" is connected with a "HMC - Hardware Management Console", so you can configure it over this (very normal xSeries-like) Linux/Windows-Server.
If not ordered with that, second possibility is a "Green Screen-Terminal" with "Twin-Axe-Cable" and a Connector to a 9-pin-Adapter-Card in a PCI-Slot of the 515.
That is the normal "first" output device for a "AS/400" (or modern names).
So, if you have such Terminal-Adapter, plug everything in and get after IPL of V5R4 the output.
It's possible, to deactivate it with deinstalling this card and priciple possible to activate LAN over the integrated little green Display and the service-buttons, but that's lot more complicated.
here you can get a lot more infos:
http://www-01.ibm.com/support/knowledgecenter/POWER5/iphc5/9407_515_landing.htm
and I will try to send you a PM.
Mark