You will have an enormously easier time of it by figuring out the pixel dimensions you want in Cyberboard, resizing the BMP to that size in whatever editing program you're using and then importing the BMP at the correct size, into Cyberboard.
If you don't have any editing program at all, think about Photoshop Elements ($100 or less, all platforms) or GIMP (free, originally for Linux, but I think with a PC edition), either of which can do what you want with ease. PC people will have to tell me whether Paint or something else can do it as well.
