Sometimes you can re-install a program successfully, then it can be uninstalled properly. Other times software houses realise they have gone wrong and offer a program or procedure on their website to do it (best example here is norton/symantec who regularly scew peoples PC's up in this way.
po'gril solution will just remove the reference to the unistall as far as I can see - the other method is to search the entire registry and delete ANY reference containing the word 'nero' - carefully. As you do it, note the names of any DLL's that are referred to in the registry and at the end, delete all those DLL's from any Nero... type directory you can find, and from System32. To be honest, you really need to know what you are doing there, as some DLL's might be common to other software too, resulting in problems with them instead. If in doubt, leave out....
