I have been asked to extract a short video film (a very precious wedding
> video) on VHS cassette into a 21st century format so it can be viewed > again.
> I need to decide whether to send it off somewhere to be done
> 'professionally', or DIY it?
If you decide to get it done professionally then the easiest thing is to take it to your local BOOTS the Chemist. They have a "Movie Magic" service to digitise VHS etc and put it on a DVD or USB memory stick although it's not obvious that they do as it's not well advertised being included in their "Photo-Scanning-Service" see:
formatting link
Be aware that if the wedding video was professionally made then you will need to be able to prove that you have the permission of the copyrite holder before a reputable copy service will touch it.
Alan