plotting the lognormal density curve

I am trying to plot a lognormal density curve on top of an existing
histogram. Can anybody suggest a simple way to do this? Even if someone
could just explain how to plot a regular normal density curve on top of an
existing histogram, it would be a big help.

Also, is there some way to search through the R-help archives other than
simple browsing?

Thank you so much. Your help and time is greatly appreciated.