Today's video technology will never match a good transparency, but there are a few things you can do to improve it. First, understand that video likes blues and greens better than reds and yellows. So if you have a choice, shoot things in the blue part of the spectrum. That may sound silly, but you can control a lot of what you shoot. Ask your subjects to wear flattering blues and greens, for example, not reds.
Video also likes light.
A slightly underexposed slide may be richer and deeper in color, but underexposed video is just bad. You can use filters with your camcorder much as you would with your still camera. Used properly, a polarizing filter can reduce glare, darken skies, and improve color saturation. Simply put, it tells your camera what's white. It then electronically balances red, green, and blue to a proper rendering of white.