You've made one error :
You'll only need the "855gm-fix"-PPA to install the fixed kernel-modules. The "libdrm"-PPA includes an updated libdrm which is necessary to install the updated intel-driver from the PPA.
sudo add-apt-repository ppa:glasen/libdrm
sudo add-apt-reposority ppa:glasen/855gm-fix
If you want to install the updated driver, you also have to include the driver PPA :
The updated intel-driver is no "must", it's nice to have.
sudo add-apt-repository ppa:glasen/intel-driver
The updated intel-driver works only with KMS and will crash if the kernel is booted without it (i915.modeset=1).
To get around the black-screen-issue you have to use KMS or, when using UMS , you have to use a modified xorg.conf-file with the following content :
These lines tell the Xserver to ignore the external VGA-adapter when initializing the driver. You can't use an external monitor any longer but the crash (Black screen) at startup disappears.
Option "Ignore" "true"
Additional notes to the package "855gm-fix-dkms" :
The patch included in the updated kernel modules slows down the graphics performance. In most cases you will only notice that e.g. scrolling in Firefox is somewhat slower. OpenGL and SDL-based applications seems not to be affected.
I've made an experimental package (named "855gm-fix-exp") which disables a function in the patched modules. This functions normally ensures that the cache is correctly written. The function is also the main source for the slowdown. Without this function graphics performance is nearly normal again.
On my notebook the modules with the disabled function work normally. This means it had no crash in two weeks, but i can't insure that it will also work stable on other hardware.
You can test the package but if your hardware is less stable than with the normal package, please stick to the normal package.
If you don't want to fiddle around with the configuration, you can try my custom Live-CD :
Live-CD of Ubuntu 10.04 with updated Intel-drivers and 855gm-patched kernel-modules