I suspect that the de600 is causing the trouble. It is unsupported on this platform.
Please try removing it. It is possible that Tru64 driver support does not exist in the V4* installation disk you are using, but does exist in V51. If this is the case, then the controller is ignored by V4, while V51 attempts to turn it on. It is possible that turning this newer PCI card on may wreak havoc on the PCI or system busses for this slightly older platform.
Some unsupported cards work on some platforms, but this might be one of those other cases.
If the above does not work, I suggest treating this as a hardware troubleshooting issue:
1) Remove all hardware except that which is absolutely necessary for installation (one memory module, one or two disk controllers, one hard disk and one CDROM, for instance). Take special care to note which I/O adapter is in which PCI slot, as you'll be replacing them in exactly the same slots later.
1.5) If installation does not work with the minimal subset of hw, you might have a problem with the installation media, or transmission, or devices.
2) If installation works with this minimal config, start adding hardware one piece at a time and booting the installation media again. Repeat until it fails. At that point, you have a pretty good idea that the last component you added is the cause of the failure. Try to add the PCI cards into the same slots you pulled them from.
3) If you determine that a PCI adapter is to blame from the above experiments, but you really want to use it, try moving it to different PCI slots. Sometimes this trick will work to get an unsupported card to work.
One end of the motherboard or the other might work.
4) It might also be made to work by removing or moving another card. Sometimes, an unsupported card might work fine by itself, but another card on the same bus might trigger bad behavior. You might be able to use "show config" or "hwmgr -v h" to see how PCI slots are arranged.
