Regarding the centre option, what resolution is your screen? When the centred option is active what gets centred is a 960px div (slide image and comments column). If your resolution is on the lower end the div might take up the whole width of the screen, cancelling the effect.
I've made comments optional now, and the second column is only displayed if comments are enabled and/or captions are shown to the right of the image. With comments disabled and captions either off or above/below the image you should see the effect of enabling centred images.