Yes,
When you are using Photoshop 5.5 you are prabably in Image.. (Mode)... (RBG Color) while doing your image. When you have all the layers and have your image to where you are happy then go to Layers... and (Flaten Image)... Then go into Mode ... and chose (indexed color)---this changes it to 256 color. Then go to Layer and make sure that
you don't have the option to (Flaten Image)if you have the option flaten it if not save file as (C.O.s callsign.bmp) That should do it!...