Do you have a component (3 video + 2 audio) cable? A normal composite cable is just 1 video + 2 audio (yellow, white, red). I got a universal component cable about 2 years ago that has three connectors... ps2, xbox, wii.
When using a component cable, you'll need to make some changes in the console's system menu, at least for the wii and ps2 (I don't have an xbox) to get a better picture. For example, I think the ps2 has an option for progressive scan. The wii has something similar plus a widescreen setting.
Once you get the console end squared away, you'll want to put your hdtv in "game mode" to eliminate filtering and smoothing, which causes lag. Usually game mode is just a brute force scaler for speed. Note that some hdtvs don't have game mode, so check your manual.
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