...Is it possible to do this? I need to make some for a fest submission but this being my first submission, I didn't have the foresight to take stills of my shots while filming.
Change the preview output to Best / Full, then click the little floppy disk icon over the right corner of the preview window. This will save the frame you see in the preview as a still image file.
Photozoom Pro is absolutely the best resizer I have found. What I do is capture my stills from Vegas, resize them to half height, thereby eliminating the interlace lines, then from Photoshop, export the still directly into Photozoom Pro and resize it to the size I want, using a vertical value of twice whatever I use as a horizontal value. It works better than any other technique I have tried.
Having said that, it's always a good idea to take a good still camera with you on every shoot and shoot any stills you think you will need for promotional material. I think we all learn that one the hard way!