I assume this is a transparent gif image - correct me if I'm wrong.
A lot of times when you use transparent gifs you get the weird staircase thing because of the way the program is interpreting the transparency pixels. It makes each pixel either 100% on or 100% off rather than feathering the pixel transparency. For instance if you had a black pixel on a white background with 50% transparency it would be grey but since the program doesn't do 50% transparency it will be black and 100% opaque.
Solution is either make your image a flat jpg with the background color you are wanting, create the logo in flash, or create the logo as a psd and import it into flash. There may be other ways but these are a few.