So, based on what you say above, this one http://www.ebay.co.uk/itm/Sun-Ultra-Enterprise-2-Workstation-UltraSPARC-II-296MHz-128MB-RAM-/230994413805?pt=UK_Computing_DesktopPCs&hash=item35c85708ed also looks "pretty responsive", but I still don't know how old it is or what I may need to go with it. I had a quick look at that forum, but I don't know how long it will take to find out what I need to know. Of course, I have got lots of other expenses. My social life is in ruins at the moment, so it would be a good idea for people on here to tell me why I don't really need to buy a Sun or Silicon graphics workstation.
You want to hear why you shouldn't buy one? Because Unix is, more or less, Unix (except for AIX which I gather is like Unix as implemented by space aliens from mind-probes of Unix-hacker abductees, but I've never used it.) Solaris is about like Linux or FreeBSD when you get right down to it (though CDE is the only desktop environment/application suite I've encountered on Unixoids that I thought had been at all designed with a serious or professional eye towards a good user experience - but then, it's also a very very 1994-vintage user experience.)
If you
do want to pursue this, though (and that Ultra II is a hell of a deal if it works, and not much of a risk if it doesn't,) you will need, at a minimum, a serial null-modem cable so you can run a terminal emulator for console access on your PC or Amiga or whatever. More ideal would be a Sun keyboard, mouse, and a 3W13-to-VGA adapter plus a 1280x1024 display (Sun's output seems to be pretty compatible with modern displays - I had to do some hunting to get one that supports sync-on-green for my VAX, though!) Those don't tend to be terribly expensive, but of course that all depends on just how tight your finances are. You could certainly use it serial-only until you can afford them. You may also need replacement install media if someone removed the OS; I don't know anything about that, you'd have to talk to the Nekochan guys.
Addendum: you'd probably need replacement install media period if the seller doesn't have the root password for the current install.