Graphical glitches

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http://askubuntu.com – So I just installed Ubuntu 12.10 from the Windows installer (dual-boot). Ubuntu seems to boot fine until it gets to the login screen. There are small graphical glitches in the screen and whenever I move the mouse, it becomes even worse (I can barely see anything on the screen). I run it on a mini-laptop with AMD athlon 64 processor and ATI radeon graphics. It seems to be a problem with my drivers, but I am really new to Ubunto and Linux and I can't find how to solve my problem (I know very little about the terminal since I used cygwin for ssh communications with a server). It is not connected (HowTos)