Cacti is in the epel repository, so if you have that configured it is just 'yum install cacti' and you are pretty much done.
This box is CentOS 4 and has some web hosting software on it. Due to exclusions its not that easy. ;-(
I manged to make this work with just plain MRTG which was on it already.
/home/../domains/../public_html/systemload/mrtg.cfg
WorkDir: /home/../domains/../public_html/systemload/ Title[index]: System Load PageTop[index]: <H1>Load</H1> Target[index]: `/scripts/sysload.pl` MaxBytes[index]: 300 Options[index]: growright,unknaszero,nopercent,gauge,noinfo LegendI[index]: Load: LegendO[index]: YLegend[index]: Load XSize[index]: 600 YSize[index]: 150
/scripts/sysload.pl
#!/usr/bin/perl
my $load = `cut -d" " -f2 /proc/loadavg`; chomp $load; print "$load\n"; print "$load\n";
May not be perfect but it works. May needed to be tweaked a bit yet too.