Can anyone describe this thing called fillrate limitation. I know how to detect it but how do I get rid of it? Buy a new grfx card? 
Fillrate refers to how many pixels your video card can draw. If the window is too big, or you are drawing a bunch of objects that almost fill up the screen, that requires a lot of fillrate.
You can make your window smaller, or try to cut down on overdraw by culling objects that will have other objects drawn in front of them anyway, which can be pretty complicated.
Or you can buy a faster graphics card.
j