If you have problems playing a show (especially when it's not running smoothly), very often the resolution of the pictures is the problem. Pictures from digital cameras have a very high resolution, much higher than the resolution your screen is able to display.
To display them on your screen the software has to scale them down which costs a lot of resources and especially on older computers this function tends be the source for these kind of problems.
An easy way to solve it, is to scale the pictures down to the resolution of your screen. This reduces the processing load quite a bit. If you have a screen resolution of 1280x1024 (19" TFT) you should reduce the resolution of your pictures to this.
The conversion to pictures with a lower resolution can be easily done with AquaSoft Barbecue an integral part of AquaSoft SlideShow Studio. It allows you to edit, convert and rename an unlimited number of pictures in one go.
If the above instruction don't help to resolve the problem you should check your antivirus program and firewall. These kinds of programs check each file which is accessed by another program and so produce quite a lot of processing load. So it could help do deactive these programs while playing a show.
It is also very important to always use the most current drivers for your graphics card.