Hints for DIY: Many dns servers use simple flat files called "zone files" which contain the data to setup the DNS, both fwd and in-addr (reverse). Check the documentation to find the location of the actual zone files, make sure you have permission to edit them (use PHP to load them into a form or editor and save) then update the SOA or serial, run whatever the command is to update the DNS cache and propagate the change if you want faster time to live (TTL) than the default.
Requires knowledge of DNS. Most *nix uses Bind for the nameserver daemon.
I posted this so you know the right basic terminology to find scripts or create your own.