I made a gothic-girl. I made her dress a little bit transparent to make things a little bit more exciting ;) I rendered her and saved the picture. Now i send it to a friend of mine, but he could see her whole body through the dress while i could only see a little bit.. how is this possible?

Could be differences in the gamma settings. Could also be differences between color handling across platforms. I have rendered pictures on a mac and had them appear differently on the pc. Pictures with gold/orange lighting seem to become more cooler on a pc. See if your friend has the same color res that you have.

platform is win 98 instead of my win2k res is different but color depth is the same. but i don't see how brightness i going to change anything in the picture itself. I mean the picture could look brighter or look darker, but the transparency of the her dress was different. Transparency is something you "burn" into the picture when you render it... strange case this is.