I've had this happen too... I have heard that it sometimes happens when you have to many objects on a lot.. That doesn't explain the cas screen though... After mucking around with my graphics settings a bit I found that on the highest texture setting my sims are blurry and my objects look great but if I set textures to medium... My sims come back to normal and I loose a little bit of quality on the objects... not hugely noticable though. I can live with them...:-P

Don't change any of your other setting from the highest level, just your textures and see what happens... Obviously it's a 3d card issue... But I have found that the quality with textures on medium is still good so I'm not going out to buy a new one..