It is generally a good idea to give your threads more descriptive topics (eg: "ot question: colds").
You can still infect others with a virus long after the symptoms have died down (relatively long, anyways; depends on the nature of the virus). Some of the symtpoms from common virii like colds are actually part of your immune system's reaction to the invasion. I know that fevers are usually caused by the body raising it's temperature so that the white blood cells can work more effeciently (though so do the invading entities
).
I
think that a common cold is not infectious for too long after the symtpoms go away, though I do not know how long it takes.
Generally, maintaining a healthy, well-balanced diet will allow your immune system to operate at peak effeciency, and can allow it to prevent an infection in the first place. It will also allow the infection to be fought off more quickly. Daily vitamin supplements can help, but you have to be careful not to take too many vitamin pills, as too many can actually do more harm than good.