Ok. I found out the main issue is the high resolution of the texture maps. These are 4000x3000 pixel and they exceed my memory capacity. Still this is a litte strange, because I have 2GB 667MHz RAM which should easily be sufficient for these textures, shouldn't it? Also I created a 2GB swap file on one of my drives.
When I reduced the texture resoluation by 50% with irfanview they seemed to load just fine. Only the eyebrows remained shaded  like in the above image. I got rid of this problem by deleting the shading group for the eyebrows in the Maya Hypeshade. This deleted the superfluous polygons at the eyebrows and revelaed the underlying texture.
Still reducing the texture resoluation is not what I want. I need the detail of the skin texture so I am searching for a way to keep it and work around the memory issue. Any ideas?

Unfortunately I can't register in the T4M forum, because the graphical confimation code is not loaded. Right now I am experimenting with a little program called Grouper 1.4 and see how it can help me. Also I found this website which seems more uptodate with adding comptaibilty between Poser and Maya than T4M.