We have blocks of IP now what we want is that a user interface where users can login and setup the Reverse DNS for there IP's, see netflow and mrtg graphs online.
Can anyone suggest if there is any control panel or script for that.

Thanks

Depending on your budget you should take a look at ubersmith DE. If you're looking for something free you could try cacti for stats, northstar for IPs and run a front end web interface for your dns servers like we do.