I can Draw Contourlines on my .img-(raster)file but i don't know how to save them into a separat Layer. I don't know where/how ArcGis saves the contourlines that I draw with 3D-analyst. I use Arcis10
Please use the Contour geoprocessing tool. I'm guessing your using the interactive contour tool from the toolbar which only creates graphics. Technically you can convert graphics to features, but it's much easier to just run the tool.