Video Capture Always Too Dark

Using a new Canon ZR-500 and a new firewire card and cable, I played my little movie into XP's Movie Maker. Unlike the bright and correct video in the camera, the video shows up on the computer as very dark. At first, I thought the problem was Movie Maker, but I got the same result with two other programs. So, I figured it had to be the cable. Nope. Same dark result with another new DV cable. Playing the video into the TV was perfect, just as in the camera, so the camera and tape did not seem to be the problem. It had to be the common link between camera and computer, I mused ... the firewire card! Alas ... no cigar. Same problem with a new card ... dark video recorded on the computer. So, now, I am completely at a loss. I have no clue. And I can't understand how all these people on MySpace and YouTube can do it so easily ... record a little video with normal brightness and contrast. What am I doing wrong?!