The simplest way that I have found for enabling task manager, registry editor, hidden files and a lot others is Regain Power. You ca download it from Source Forge and it is completely free (I think it is open source).
I agree with you that there may be rogue tools containing viruses cool_jatish but the tool that I am referring to is an open source project hosted on source forge. This means that its code is available for anyone to inspect which rules out the possibility of it containing viruses and the likes.
I also dare to say that there are times when RUN is also disabled so some of your tricks may not work or the procedure would be different because you would have to regain access to the Registry Editor and then from there enable Run.