Acer Aspire One 725 - missing graphic card driver?

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http://askubuntu.com – Recently I bought an Acer Aspire One 725 Netbook and installed Ubuntu 12.10 on it. I bought it, because it can run HD movies and has Full HD on external VGA port. However, movies from youtube have a really slow framerate. If you open three tabs in Opera (for example g-mail, youtube and askubuntu) it gets really laggy. My suspicion is that the driver for graphic card is missing. When I check the "System->Details->Graphics" the driver is unknown. After running "lspci | grep VGA" I get this output: 00:01.0 VGA compatible controller: Advanced Micro Devices [AMD] nee ATI Device 980a From what I (HowTos)