Both have the same-looking RGB plugs, by messed up, I mean three columns
   of what should be one column, with a raggedy looking sync problem.

The HP monitors and video boards are all single-frequency as far as I
know.  Probably the monitor you're trying to use isn't the correct
frequency for the video board in that machine.

   So...  I'm trying to boot it via the serial port.  Does anyone know what
   settings to use for speed + parity, etc, and what should I expect to see on
   my terminal?  I tried 9600bps ? parity, and got '@' and that's it...  Yes,
   I am using a null modem cable.

The kernel definitely expects 9600 baud.  When you say you `got '@'
and that's it', do you mean that's all you got after turning the
machine on, or all you got from the kernel after it loaded?

You may have to unplug the video card or use `options DCACONSOLE=0' to
get the kernel to use the serial port.