dpkg-reconfigure xserver-xorg would probably be an easier command to do an easier switching of graphics drivers. Mainly because linux newbs might not know their way around an xorg.conf file itself. Plus in dpkg-reconfigure xserver-xorg, it'll give you a list of graphics drivers to select from, so you can at least see if you have the right driver on your machine to select from besides the vesa driver.
Again aardwolf, what graphics card you have? If it's nvidia, then download the nvidia-glx driver. If ati then download the fglrx driver. And then do dpkg-reconfigure xserver-xorg to select the proper drivers. After the settings are applied just restart your machine. Or just restart X (i don't suggest this in kubuntu, kubuntu has a funky way of restarting X).