SaigonK, RTFM on MRTG and you'll find that there are configuration variables to decrease the internal sample interval below five minutes, and just configure cron accordingly. If you need to update a little more frequently, MRTG can do that. If you need a lot more frequently (approaching real-time), then MRTG is the wrong tool for the job.
If I'm not mistaken, five minutes is the internal stats window for a Cisco device, and many others copied that behavior, so some stats will simply not be measurable at a finer granularity.
The version of MRTG that comes with Fedora Core 1 is dead simple to get running, just run cfgmaker and indexmaker and put the output into /var/www/mrtg and edit WorkDir.