okay, here is my update :
the script for the creation of the bootimage went through without a hitch and I was able to boot up an configure my MD (asrock ion330). At first I had some trouble with the AVWizard, but I got around that. Then I tested the available UIs but went with the basic one, since the latest nvidiadrivers weren't activated.
After the orbiter generation was finished, I went to the KDE-Desktop, opened a terminal and used nvidia-xconfig there. After that, a reboot, AVWizard and I could use UI2 with Alphablending. I didn't have the sound over spdif optical working, so I went to the desktop agai and performed the Alsaupgrade with the script I posted here earlier....works fine now
I was however curious and did a apt-get update and a dist-upgrade. Interestingly enough there were some repos offline and there were some files relating to mythtv that had been downgraded (!?).
Later that evening I tested mythtv with VDPAU, which was not quite nice...choppy performance and quite unstable. I also read, that xine should also come with VDPAU- but so far I have not been able to see in in action...I tried some HD-content I had waiting on the disks, but I also noticed a rather choppy playback.
Tonight I will just scrap the current MD and create a new one. I want to try and see how it works out of the box- in other words without the aforementioned updates.
Other than that, nice works, guys :-) you are my heroes!