This is a noob question but when i try to import monsters it says that it's the wrong size what size is needed?

Odd. From my experience working with 2k3 there is no file size limit for the monsters. Did you set the image at the right bit (should be lower than about 64 colors I think)?

Actually, thats 256 colors, and I don't believe that is the case, it actually tells you if it's a color or size problem. There is a size limit to just about everything RM2K3. What size are you using? Try something quite a bit smaller.