ATI Mobility Radeon X600
2D acceleration is supported by the "radeon" driver in X.org.
Display on the internal LCD works as long as you set the monitor settings correct.
External VGA port
There are known problems. The driver from ATI turns off the switching between internal and external port. Workaround: Don't use the ATI driver if you want to use this feature - use the VESA driver instead.
For Ubuntu Dapper read single/dual/cloned screen - should work fine.
Proprietary ATI driver
The fglrx driver adds 3D acceleration.
Type the following commands after you have loaded the fglrx module:
# aticonfig --initial
# aticonfig --overlay=opengl
Linux kernel Framebuffer driver
Supported by "radeonfb" for console, but conflicts with X.org when using "radeon" or fglrx.