I noticed that enlarging a video of Real Player format causes pixellation when using my GTX 470.This only happens by Real Player videos,when I open a video of another format there's no problem.I first thought it was a problem of the player,but when I installed it to another PC it works fine.So I tried changing back to ATI X1600 and the pixellation problems went away!
Is this a fault of my card,or does anyone else with a 470 have this issue?
Could be funky drivers. Seeing that you put in an ATi card in to test it, that means you have the drivers also installed onto the system. This might cause a problem with the nVidia drivers. Try uninstalling the drivers and do a clean sweep of all drivers then reinstall the nvidia drivers.