Having a cold won't have a significant effect on your metabolic rate, so your calorie needs remain the same as long as your level of activity stays the same. If you are less active because you are under the weather, your calorie needs will decrease accordingly. If you don't have a fever and you feel up to it, though, its fine to engage in your regular exercise routine. Exercise can help stimulate the immune system and may also help clear up congestion. If you're sharing equipment with others, though, be a peach and wipe down the equipment with disinfectant after you use it to prevent spreading your cold to others.
In terms of your nutritional needs, the immune response that's causing the stuffy nose and sniffles is also increasing free radical activity in your body. Foods that are high in antioxidants, such as fresh fruits and vegetables, can help to clean up the extra free radicals. It's also a good idea to avoid excess sugar when you're fighting something off because sugar tends to depress the immune system. (Actually, it's really ALWAYS best to avoid eating a lot of sugar.)
Source: Nutrition Data