[R] summing values by group

[Larry White]

At the risk of being wacked for asking what should be obvious....  

I have a data frame with one categorical variable "CAT" and several
numeric variables.  I want to be able to get simple statistics on the
numeric variables by level.  For example, just as you can use table
(CAT) to get the counts, I'd like to be able to get the means and sums
by category.

If someone could point me in the right direction, I'd appreciate it.
I've been through the SimpleR and Using R for Data Analysis... docs
and I'm still clueless.

thanks for your help.