Hi Billy
1) Cacti is the simpliest : scripts already exist and can be used "as is", an interface allows you to modify many parameters very simply. MRTG is too old and doesn't have all the capabilities
RRDTool has (Cacti is in fact an interface to RRDTool).
You could also think of installing RRDTool alone and create your own scripts and commands to create db and graphics. You can also use an other "interface" to RRDTool. I personnaly use
MRTNK, a package of scripts that allows to use RRDTool as (or almost as) MRTG.
2) MRTG and RRDTool can use SNMP OIDs or scripts to obtain the values they have to draw.
3) When i was using MRTG, i had the same graphs as those i have today with RRDTool (in fact, i have now more graphs as RRDTool can use negative values and MRTG can not).
4) There are two howtos : one in
english and a more recent one in
french5) Have a look at this
howto6) It is not an obligation. I don't like SNMP and i use only scripts. If you are interrested, you can have a look at
my MRTNK (RRDTool based) page.

Sorry for my bad english, i hope you have understood.
