LimeWire makes the maximum height 40 pixels smaller than the height of your screen, in case there's a dock or something at the bottom (as there is on Windows & OSX by default). Very unfortunately, there's no way for us to figure out where the dock is, or get the screen size without the dock.

You can, however, make LimeWire larger by manually dragging it. The catch is that next time LimeWire is started, it'll size itself somewhat smaller.