Strange lines and glitches appearing on screen on a Macbook
Well, it looks like you may need a visit to the nearest Apple Store,
but first try downloading SMCFanControl: http://www.macupdate.com/app/mac/23049/smcfancontrol and try turning up the fan speed to cool the overheated graphics card and see if that helps.
Please note that I am not sure whether the fan speed on the MacBook is adjustable, but it's certainly worth a try.