I'm posting this question actually with an answer so as to maybe help others who have experienced it. Now, please keep an open mind...
I recently purchased a new HP notebook running Windows 7. I like the PC however from the "word go" its had one very annoying problem - the screen will constantly dim and then flick brighter again. I have gone through all control panel settings i.e. power, display etc all set to 100% and trouble shooting. Also used the HP setup manager etc, problem still occurred.
This would occur while using the web and navigating between pages and tabs etc i.e. reading a webpage became extremely annoying - the screen would CHANGE BRIGHTNESS for no apparent reason. Then I realised this flickering would only occur using the web, it never happened with other programs like word, Open Office, Notepad, games or other programs - this helped me in some ways, I was able to possibly isolate the problem and find the cause.
If this is happening to you, try seeing if this occurs while your using the web and no other programs. If so, you may want to try a different browser i.e. firexfox, chrome or something. I don't know if I've done anything else but that constant and annoying flicker has gone away.
Short answer - Google Chrome has fixed the problem.