[CentOS] looking for graphing tools

Hi!

I have bazillions of incoming (rejected) attempts to connect to my
SMTP server, and I'm interested in separating out those that seem
to come in huge bunches (e.g., the one from yesterday that ran for
about 10 hours and sent over 4100 attempts), and graphing them so
I can see the spacing and/or distribution in time.

I can figure out some simple scripting to turn the maillog entries
into times since the epoch, or other formats, if needed, but I have
no experience with the various graphing tools availabe, or even
what (or where) they are.

I'd appreciate pointers-and-or-advice, should any of you have any
such things to give.

thanks in advance!

Fred
-- 
-------------------------------------------------------------------------------
    Under no circumstances will I ever purchase anything offered to me as
    the result of an unsolicited e-mail message. Nor will I forward chain
    letters, petitions, mass mailings, or virus warnings to large numbers
    of others. This is my contribution to the survival of the online
    community.
 --Roger Ebert, December, 1996
----------------------------- The Boulder Pledge -----------------------------