[Steve Carlton]

I think you're fighting a losing battle. Some suggestions in order of preference, and test the setup to confirm:

1. Get an SB600 + a diffuser. (An SB800 includes one)

2. Get or rent a 50mm f/1.8 lens. They're about $125, and they're an awesome value and very good to have. Fantastic image quality. It might be fast enough to shoot without a flash (try ISO 800 and auto WB) It won't cast a shadow when using the built-in flash.

3. Shooting with the built-in flash should work to some extent. The more the 18-200 is zoomed in, the bigger a shadow it will cast against the flash. Wider angles might work. Get a diffuser if you can. Set the white balance to flash and the ISO as low as it will go, and put the camera in program mode.

4. Set your ISO high, like 800, and shoot at aperture-priority wide open. Shooting ISO 1600 or more will probably result in bad image quality. Hopefully, your shutter speeds won't be under 1/30th sec. Zooming will slow down this already slow lens. Set your white balance to auto. Try some test shots.

If you've got the D70s and an 18-200VR, you really should add an external flash to your bag. Setting your EV (exposure compensation) to -0.3 to -0.7 or so will reduce the shutter speed requirement and probably avoid unnaturally bright exposures, too.