Yes, however the quality will not be very good. The images will be 720 * 576 pixels in size and soft compared to the originals.
If this is a commercial DVD then you need to check out the copyright / licensing for use of the DVD. In most cases you are not allowed to 'rip' the DVD or use extracts withour permission.
If this is a DVD you have created - do you have the original source material used? This will be of better quality.
If not you will have to copy the VOB files from the DVD to your computer, change the file extension from VOB to MPG and import them into Photostory - you do not have to convert them
Once you have done this, in timeline mode, position the timeline cursor at the point where you want to capture the image and select File, Export, Single frame as jpeg, fill in the file name and location and export it.