If you just want to save a SINGLE frame, easy. Place the cursor at the frame you want to grab, be sure its in the preview window, if you feed to external monitor, turn that switch off first. Now click on the little floppy icon that's above the preview window. It can either save to a directory on your hard drive on be used from the clipboard.
If you want to save a sequence as a series of stills from the timeline as a bunch of JPEG's, no not directly from Vegas AWINO. You could save a range as AVI then convert to JPEG's, several applications do that. Can't think of one right now.