Scott told you absolute truth in everything above but omitted one factor. The VT440 and VT540 both utilize the same 160w SHP lamp but the SVGA VT440 has a higher "fill factor" than the XGA VT540. "Fill factor" is the ratio of active (transparent) panel area over inactive (opague) panel area. In other words, the lines between pixels are the same width, and therefore the VT540 has more total line area versus pixel area and absorbs more light from the lamp. This is why the VT540 is rated at 1000 lumens brightness and the VT440 is rated at 1100 lumens. In fact, you can only see the difference side-by-side under the exact same ambient lighting while using the exact same source - whereupon the VT440 is slightly brighter, but the pixels are also bigger. The advantage to the VT540 is you can sit closer, getting more of the "big screen" emotional impact, without noticing the pixel structure. Another VT540 plus is it will scale all the HDTV modes - you need XGA or better for decent HDTV, which could matter to you at some point.
Gary