Assuming that your screen is on a CRT monitor, I don't know of any way for the video card to have that effect on the monitor. On the other hand, inside the monitor there can be multiple adjustments for Vertical Linearity. If one of these adjustable circuits is going bad, that's one of the possible symptoms. Sounds like new monitor time to me. Of course, if you are using the top of the monitor for a bookshelf, and blocking the vent holes, then the problem could just be overheating. NB: The long term effect of overheating is reduced lifespan.
Just wondering if anyone can help with this? Lately, I have been having video problems in that my screen has been "squeezing" a bit so that the top and taskbar will get thinner....then go back to normal. It happens sporadically, almost like it is being compressed. I have the most up-to-date video driver. My card is an ATI Radeon 9000 Pro 128MB. I have a blower underneath the card in a PCI slot getting rid of hot air. This has been working great for about 8 montyhs with no problem. The blower is still working fine as well.