You can change the size and scale of your output presentation to make it fit your webpage design even smoother. To do so, just enter the dimensions that you need in the Advanced tab of the Publish window, and your Flash movie will adopt the size you want. If you are not sure about the pixel format you need, you can try to play with the scale, which will calculate the presentation size for you.
iSpring Pro also supports custom aspect ratio for slides that you can set in PowerPoint.
Keep in mind that changing the Flash movie dimensions will effect the output file size.