Log in to v20z console using serial management

Did you try a null modem cable in the middle? I think that the Sun wants a real terminal.

First off, what models are they -- The little one on top looks like a Netra of some kind. The big one is obviously an Ultra Enterprise 4500.

Second, quick crash course on Sun hardware, probably applicable to the box on the bottom more than the one on the top:

• As others have pointed out, if you want to use video you need a 13W3-to-VGA adapter (or a Sun/13W3 monitor).
  You also need a Sun keyboard - If you don't connect a keyboard…
• …You can use a serial console (or HyperTerminal on a Windows machine).
  • Connect a null-modem cable between serial port A on the Sun machine & your Windows box or serial console)
  • Open up HyperTerminal & set it for 9600 baud, 8-bit bytes, No parity, 1 stop bit (9600/8/N/1).
  • Turn on the Sun machine. You should get dumped into the Sun boot monitor (and if an OS is installed, eventually a login: prompt.

From there an OpenBoot command reference should get you where you need to go in terms of getting the OS up and running or installing a new one.
If you don't want to run Solaris I would encourage you to consider NetBSD or OpenBSD - I'd lean toward the former if you expect to get a lot of heterogeneous "inherited" hardware, as you can install NetBSD on pretty much anything.

Beware of sending the break character once the OS is started (this often happens when a serial console is turned on, or when some USB-to-Serial adapters are plugged in). This will cause the machine to drop back into the boot monitor (suspending the OS and leaving you at an OK prompt) -- Should this happen to you inadvertently, just type go and the system will return to normal operation.

Assuming the box on top is a Netra it's a bit different -- There's usually a combination serial and Lights-Out-Management (LOM) port that you connect to with a Cisco-style console cable (9-pin to RJ45). This Page has instructions on fabricating one, but you can probably buy the cable for a small pittance and save yourself the work.
This page talks a bit about how the LOM system works (basically type #. (hash period) to get into it and it's a stripped-down equivalent to the boot monitor with some other capabilities).

Of the two the bigger box is likely to be better/more useful, assuming it wasn't stripped of all components of value.

Note: Some Sun hardware only has one serial port, marked "A/B" (I think the 4500 may be one of these but SunHelp disagrees) - on the off chance it is, I believe a regular serial cable will hit port "A" which is what you want. SunHelp's serial ports and pinouts page is also a great resource, as is the rest of the SunHelp site.