To use MRTG on my personnal Web site, i downloaded from
http://rpmfind.netucd-snmp-4.1.2-8.i386.rpm
mrtg-2.9.10-1.i386.rpm
libgd-1.3-4.i386.rpm (mrtg depends on it)
sysstat-3.3.6-1.i386.rpm (for CPU usage)
I installed all these packages in that order and it works very well.
To use ucd-snmp, you'll probably have to rename the smnpd.conf file.
Regards.