You could also use something like GoldenGate to capture changes in oracle and apply them to the mysql database , although if this is the one use case you have, the cost of the product may not be justifiable, in which case probably just a simple perl/php/python/etc script would do the trick.
I've used HSODBC links between mysql 4 and oracle 9i and found the performance less than fantastic, hopefully things have improved, if that is the case, this may be a viable solution, however you would still need to do it as a job ( inside or out of oracle ), as I'm not aware of anyway to make calls from mysql to oracle.
