How do you convert an 8-bit bitmap already loaded into a handle to a 16, 24, 32 and back and forth? Please help!!!

If you have a handle then you can use the GDI to do it. Just blit it into a destination that is in the format you want. The GDI will convert it for you. Otherwise you have to get the palette then ask windows for the dib bits. I could be wrong, but I believe a dib section will give you direct access to the bitmap.