There are a few ways to achieve the veterinary nursing qualification however not by an evening course. The British Veterinary Nursing Association (Im not sure of the web address) will be able to advise you properly.
I qualified nearly 5 years ago and am not involved with nurse training so my information may not be 100% accurate but basically there are 2 ways to work towards the qualification.
1 - The degree route, this was not available when I started and there are mixed feelings about this route, personally I think that any way we can push the profession forward has to be a good thing. As far as I am aware, the degree is a 4 year, full time and holidays are spent 'in practice' to build on your knowledge during the term. I know that Langford (vet school) in Bristol and Middlesex University do this. Hopefully other nurses will read this and elaborate for me.
2 - The NVQ route, this involves working full time as a student nurse within a veterinary practice and attending college either on a weekly day release scheme or 3 month block. It is a 2 year course requiring you to build a portfolio (coursework) and undertaking oral/practical and written exams.
I would recommend that you try and get some work experience at your local practice to give you a better idea of what the job entails and the chance to speak to other nurses. Let us know what you decide!