That's pretty much what I've read. Of all the herbal remedies/treatments out there, the only one that seems to have any potential effect is zinc (not an herb, I know), if you take it lozenge form and if you take it at just the right time (i.e., when cold symptoms very first appear, which is sometimes hard to detect). The idea is that it coats your throat when you swallow and kills off the virus. It doesn't prevent colds, but can decrease their duration.

I don't know about that, but roofers use zinc-coated plates to kill moss on rooftops. You tuck them under the shingles near the peak and the next time it rains, the water washes the zinc over the moss.