One method used to register you parts is to put on each drawing in Illustrator or in Flash small dots at opposite end corners of each drawing. Or if drawing on paper, photocopy a sheet with the dots in place, when you scan in, keep the dots and you will use them to register. In Flash, you can group each drawing with their dots (or convert them to symbols) and align them with the align tool (hit center to stage button and the two top middle buttons for each part).