I read a tutorial that said to start at 300x100, 72dpi and to change everything to 72dpi before you add it to the blinkie file. That didn't work for me, so I just dragged and dropped to my hearts content, saved the psd as a 300x100, changed it to 72dpi and shrunk it, and then animated it. My first attempt at a blinkie is in my siggy (for me and Jenny for ADSR3).