Is there a Dynamic DNS Client to go with MyDNS? One that I have come across that looks pupular is ddclent which is used by a few service providers. What I am not sure if it needs some additonal server side software besides the DNS server itself to be functional.
I'm not sure how ddclient communicates with the DNS servers, but basically you just have to parse the output and write a little script that updates the record in the MySQL database.