If your projectors have VGA in + VGA out, that would be as simple as daisy chaining them with the source signal feeding the first one in the chain.
If the projectors do not, then a VGA Distribution Amp (ebay?) would be a relatively low cost solution.
With VGA, runs can be as long as about 100m without much loss. With other types of signal, eg. HDMI, DVI, etc. you will probably need Extenders ($$) for long runs. SDI can also have pretty long runs without loss, but SDI capable equipment are inherently more expensive (cameras, projectors, output devices, etc.).
Another alternative is a Matrox Triple-Head-to-Go unit which sees the source signal as one, and splits it up into 2-3 separate signals. This allows you to create, in say Photoshop or After Effects, or ??, a larger than single image (eg. 2048×768 or 3072×768 for 1024×768 projectors). Cabling would depend on Matrox model – HDMI, DVI. Not sure if they have a VGA model.
Good luck!
Thomas Leong