If it is just one of a few websites you visit it could just be something specific with the website. If it was your hardware it would happen all the time no matter what website you went too. You would also notice other changes in things you do on your PC. Software running slower then normal. You would also notice these grafix fluxuations in all your software and not just cetain web pages online. Personaly I think it is the websites you are going too maye something to do with you needing the latest java installed, or update your macromedia software. I would at least visit the microsoft updtae site and update my PC and go to macromedia.com java.com and shockwave.com and get updated software before spending cash on new hardware.
my 2cents.