This is a complex question, and hard to say, but I'll my best.
I have two computers I use often, but only one input on my monitor.
However... My video card has two output ports, is it possible to run the second one through my video card?
The card is an ATi HD5770.
(Or, cheap KVM switch.)

The switch would cost as much as a new monitor.

Synergy?

e: nevermind read that wrong

No, you cannot do what you want to do. Use VNC or something to remotely control/view the PC from the other one.

TightVNC worked well for me. Besides the lag I mean, I am blaming that on my crummy Celeron machine.

No, it's VNC. It will lag even on a gigabit connection between PCs.

Remote Desktop has better performance, but can be annoying due to how it works (takes over the session instead of just controlling existing session).

Ah, good to know. I did refer to what I was doing in another thread as remote desktop, when in fact it would have been VNC, which I understand is totally different. I just couldn't be bothered to figure out how to get remote desktop to function between XP and Xubuntu.

If I'm resorting to some sort of remote, it needs to be fast enough to play games well, and work with Win2k.

If it's any sort of game faster than solitaire it won't work on VNC/Remote Desktop (VNC will actually show it most of the time, but haha I hope you like slideshows and 1second+ lag).

I think you'll just have to suck it up or get a switch.

What. :/

I bought http://www.newegg.com/Product/Product.aspx?Item=N82E16817802100 this and it's worked fine for me. It was like $15 or something.

It has a bit of an odd way of switching... you HAVE to plug a keyboard into it, and then tap scroll lock twice to switch... but it works. Also once it wouldn't switch and the light on it started blinking, had to unplug it from EVERYTHING and then plug it back in to fix it. Only happened once though. Other than that it's been pretty much perfect.

[Edit: Also for VNC I recommend UltraVNC. There's also an interesting VNC variant called MetaVNC which allows for seamless windows but it's a long dead project and doesn't support Vista, unless you turn off glass maybe.]

What what? I told him his hair-brained video card idea wouldn't work. And that's a switch, which is what I mentioned...

Hmm ok his wording of his question confused me, he wants to plug one video card into the other? Not sure what that would do, either nothing will happen, or the "losing" card will be fried and need to be replaced... doubtful though, most likely nothing. Idiot-proofing and all that.

I'm actually using my KVM to switch between a Wii->VGA adapter to get my Wii on an LCD monitor at 480p and my old PC (I don't switch keyboard since the KVM only supports PS/2 not USB... maybe if I find an adapter). I think I'll eventually switch over to hooking both monitors up to my new PC, making my old PC headless (and running Ubuntu) and accessible via VNC (or some X protocol? Need to research what's possible, I know X allows remote access, cygwin can probably do something or I can find a native Windows client?) so I can pop in whenever I need to do something. Secondary monitor would still be switchable to Wii via the KVM.

So yeah that's my current and planned solutions for three machines on two monitors.

X Forwarding makes VNC look like a speed demon, FYI.

When I was running two rigs side-by-side I had a cheap KVM to bounce between the two (same thing, double-tap Scroll Lock), and I'll probably pull it out again next week when the parts for my new rig come in.

When you say side-by-side, do you mean two monitors as well?

If so, Input Director is the way to go.

Duel displays.

It annoyed me when people who played "JKA" would say "dual." They'd go, "Wanna dual?" I might say, "I dunno, wanna three?"

Last time was single monitor, but I will have two monitors when my parts come in this time.

Yes, please, when can we start?