Grab Thumbnail from Video.. but Vimeo!

Hi guys, tough one for you – I want to show a preview thumbnail image of my embedded vimeo video on my thumbnail. I can take images from my stories and show thumbnails somewhere other than the post using the ‘Custom Fields’ in wordpress, but I don’t know what I can do to either –

a) show the same video (but smaller) on a part of the homepage.. using a custom field to identify it?

b) take a still from said video.

Any help much appreciated!! really not sure how to approach this..