thanx for your replies,
maye the behavior has not changed, but the same Tiff 16bit is treated differtly from 7 to CS, 7 stores it as alpha CS applies the as transp.

Dennis,
Yes i can create a alphachannel from the layertransparency (of course) but the original background is lost,
-- think if a house rendered against a sky in 3dsmax, i want to do different operations with the foreground and the background, like masked adjustments, retouching etc..., therefore i need the alpha as a basis, but i would also like to have the original image and not only the foreground.

Of course we have workarounds like keeping 2 images one for the image one for the alpha would work but this causes waste of storage/time. Also converting with 7 would work.
we have to deal with this issue very often so a more
handy method would be nice.

for 3dsmax/mentalray there is no extra setting how to output the alpha

so
- is there a method/tool to tweak the alpha associaton?
- can you change the alpha association manually
- for CS it would be nice to have seperate channels not applied but treated as a seperate layermasks