Yes, an image can be saved from the trimmer, while in the preview window. Follow the same process as if saving from the timeline. HOWEVER - the image will have square pixels - i.e. will NOT have the DV aspect ratio applied, and when you incorporate the image into your timeline, you will need to change the properties to "match output aspect", or change the pixel aspect ratio to 0.9091 or the images will be slightly out of proportion, and will have black bars. See this thread:
I must be doing something wrong because each time I click on the save button in the preview window, it captures the frame where my cursor is on the timeline. I make sure that the last window I was in was the trimmer window. From my description, do you see anything that I'm not doing right?