I think the limit for the cable is about 100 meters (you should be able to find the specs online). You might get away with bad wiring (pairing the wrong colors) when you do the cable for small distances, but for such distances you need to use the correct wiring, and route the cable in a place that has little interference. Also, use STP cable (I think it's called like that... the S stands for "shielded") as opposed to the cheaper UTP.
Specs might have changed now... just try to get a shielded cable from the highest quality, wire properly, route properly, and reduce speed to increase reliability. I had a cable on about 20 or 30 meters, and I limited it to 10mbps - it made it more reliable.
For the distances that you can reach, you can look online for more precise numbers.
PS: I might be wrong about STP...
Although STP prevents interference better than UTP, it is more expensive and difficult to install. In addition, the metallic shielding must be grounded at both ends. If it is improperly grounded, the shield acts like an antenna and picks up unwanted signals.