I have used EZ-IPUpdate for a number of years on E-Smith and SME without problem.
Try to run it manually first to ensure it works. Setting the config file with the executable bit should be enough to figure out if yout file is correctly identifying your own settings.
Note that if you are behind a router, you MUST specify the IP as 1.1.1.1 and NOT specify any interface (no eth0, eth1 or ppp0). Because the program will only run as a daemon if an interface is specified, you will have to run it using the scheduler.
If you do not have a router between your SME and the internet, then you should specify the interface only (try either eth0 on a cable modem or ppp0 if you use PPPoE) and run it as a daemon instead of using crond.
It should work fairly easily but, not knowing your exact configuration, it is not possible to tell you exactly how to do this. You will have to do some trial runs.
Good luck.
Serge