We shall discuss what is overburning first.
Certain cd's (700mb) are sometimes allowed to be burned for only for say 692mb by cd burning softwares .
Of course you can override the burning limit and this is called over burning .
Various cd and dvd burning softwares allow overburning but the default setting has to be overridden.
Let us see how overburning can be done using nero :
Open nero express and open the more button and select configure.
In the properties window select the express features tab and then check the enable dvd over burning and enter the maximum size to overburn.(do not give a very high value the deault is 4500mb,just equate it to nearly 4.7gb)