Be sure that rrdtool ,Net::SNMP and Net::Netmask are installed on the system.
If you have error for missing RRDs module, go in the rrdtool directory and
type 'make site-perl-install' in order to install it.
Copy the cimon.conf in /etc, or edit cimon.plx to fit your needs.
Edit cimon.conf and add your routers.
Add networks if you have ip accounting enabled. 
ReadWrite community is needed for this to work.
If you want to have graphics in Bits per Second instead of Bytes Per Second
edit cimon.plx and set $bits to 1.

Quick Note about how to enable cisco ip-accounting
1.Telnet to your router and login
2.Switch to enable and configure 
3.make basic access-list to bind the read-write community + host 
access-list 5 permit xxx.xxx.xxx.xxx 
where xxx.xxx.xxx.xxx is the ip addres from wich you will
make  your querys
4.enable snmp-server
snmp-server community rwcommunity RW 5
where rwcommunity is your communitystring and 5 is the access-list
that you've created.
5.You have to enable ip accounting on the selected interfaces.
Because cisco counts only the output packets on an interface you'll have to
determine wich interace is outgoing and wich is incomming.
E.g if you have a serial interface to the internet and ethernet interface
to your local area network in order to get input and output for the accounted
hosts you have to enable traffic accounting on both of them
--------------------------------------------------------------------------------
Examples:

router#conf t
router#interface Serial0 
router#ip accounting output-packets

Will enable accounting for the output on serial interface (you get your output packets)

router#conf t
router#interface Ethernet 0
router#ip accouting output-packets

Will enable accounting for the output on ethernet interface (you get your input packets)
----------------------------------------------------------------------------------
Be sure that you completely understand how cisco makes ip accounting (this only in case
you're preparing to ask questions ;-)).
More information can be found on www.cisco.com.

Cimon + SASacct
To view the statistics collected for a period (date-to-date) you can use 
the cgi scripts from another ip accounting package called sasacct.(http://rousse.pm.org/sasacct/)
Just copy the .cgi scripts in yor cgi-bin directory and edit showtraf.cgi to point to 
the directory where the files are located, or another option, if you're using sasacct
just point the logdir of cimon to be the same as of the sasacct.
Note that if you don't have sasacct installed and running (you don't need it if you only plan to
use cimon only) when installing .cgi scripts you have to make two modifications.First is 
the location of sasacct.conf (modify showtraf.cgi) and second edit sasacct.conf
- D:somedir  must be replaced with D:/cimonss/logdir. 
SASacct provides some functionality that isn't implemented in cimon because it's already in sasacct.
This includes summarizing of the logfiles, (sasacct -s), generating graphics only (sasacct -d) and generationg 
html indexes with the graphics (htmlmaker.plx from sasacct's distribution). 

Enjoy

Buy me a beer if you find this usefull ;)). If you can't just have one and say "Cheers sas".
