Shooting RAW is great! I do switch back and forth depending on what I am shooting. When you are doing photo shoots I would definitely recommend shooting RAW. You are able to edit the photo a lot more than would be possible had you shot in JPEG only. You should always shoot at the lowest possible ISO for the given lighting. As you increase the ISO you increase the noise and lose some image quality. Sometimes you will find you just have to step up the ISO to get the shot or miss it.
ISO800 with the D200 is about as high as you would use...I shoot ISO 200 most of the time...
Check out you tube for tuition on your SB600....