Can herbal supplements boost your immune system and help you fight off the bird flu easier?

Yes. You don't need to be concerned about the bird flu, but rather the seasonal flu that we are susceptible to. Fish oil, vitamin b complex and vitamin d may all be helpful. Good dietary habits and exercise are most important for a healthy immune system.
Not proven effective. Herbal supplements are not proven effective in preventing bird flu or other infections. Staying healthy & happy, eating a balanced diet, and getting reasonable exercise, etc... May help keep one's immune system in top shape, to fight against viruses & bacteria. Some herbs, in certain concentrations, using some parts of the plants, prepared in a particular way, may help relieve some flu symptoms.