Even though I have a very fast computer, I'm thinking of turning my two older ones into render farms. My question is how good are they with still work since I rarely do animations? Will they save me time? I need to do some specific timing on the computer I have, but if the render farms  will help, I might put the older computers which are sort of in pieces to work.

Thanks in advance.

They should help.....with the caveat that the older the hardware, the less return you see. If you are talking about just a generation or so old tech, then you'll see some time savings. If they are older chips, like a P2, then they -might- work....but you could find them chewing on one tile while your main system grinds its way through have the image. What will help is plenty of memory, and stripping all the peripheral out of the renderboxes. No sound card; the driver can slow the OS down, and thus the rendercow. And if you have an on board video chip, then pull any video card that might be there; you only need very basic desktop imaging for a remote box, and that will save you power on an overpowered video card, and offload the more complex video driver.

Quote - My question is how good are they with still work since I rarely do animations? Will they save me time?

YES !
Time of rendering will be shorter.
But...if these 'old' computers is really 'low-end desktop' type that time of rendering only slightly changes.

Just TRY rendering and testing this 'render farm' with old PCs.

The 2 older PCs are core 2 duo processors with 4 gig ram on both.

Then I'd say you have a good start on a renderfarm........ :P 

Quote - The 2 older PCs are core 2 duo processors with 4 gig ram on both.

I've had mixed results with my render farm. I found it to be marginally effective. They spend so much time passing infor around the network they spend very little time rendering. They are also a background process so they dont max out your cores like a standard render does. Make sure you have a full gig connection on each PCs network or don't bother.