Windows 7 or Nvidea driver problem? Need solution

OK so I have just installed Windows 7 on my PC.
I use MPC with CCCP codec packs.

Never had a problem with XP everything worked fine. But now when I play my movie files the vdeo appears slightly pixelated.

Been to a few forums and some ppl say it's Windows 7 and you need to remove a dll file but that then disables Aero. Others say it's the Nvidea drivers and you should install an older version or the MS verified ones.

Dont want to remove the dll file, tried installing older drivers still nothing fixing the problem. Also tried chanign video renderers as some also suggest, still no fix.

If anyone know any fix to this would be helpful.