Tried it out, and sadly no solution yet.

* Tried software mode (normally Direct 3D)
* Tried 16 bit mode (normally 32 bit)
* System RAM: 512MB, Swap file fixed size of 768MB (I'm aware it is a bit too big)
* I can't tell if my probs started with 1.34, I installed it after playing with a few hours with my char and then just continued playing.
* Programs running in the background while patching: yes (eg. mysql, apache)
* Yes I am using a profile with admin rights in Win XP
* Just defragmented my hard drive and free space is about 6GB
* DirectX version 9.0b, detonator 44.03
* Read the faq but could not find another solution

I'm going to install the retail version once again, but I doubt I will be able to load my 1.34 save games. We'll see what happens. If this does not work, I will patch this new version making sure that there is nothing running on the background (will kill as many apps as possible)

Thanks again for the ideas!