Yes a web site can work. It has to be easy to navigate but not childish. The layout needs to be professional with no mistakes. Information should be acurate without gimmicks such as tunes and tacky selling tactics.
Displaying your web site address on all advertising and on the van (easier to remember than a 'phone number) will give people another avenue to check you out, and by doing so, giving people a sense of security. You are not just this bit of paper through the door, you are a reputable company... but you will only look as good as the professionalism that you show. As I said to Paul Chambers yesterday, I do not go along with the idea that any website is better than no website. Your homepage will have approximately 3 seconds to capture your potential customer, get it wrong and you loose a sale.
Use your own text, take time to perfect it. Don't steal other peoples pages (we had our first ever service page (text) stolen) which actually done us a favour and forced me to offer something even better, but it is very annoying.
Putting together a website is not a five minute job, it will and should take you a long time, you will change things many times along the way and improve on ideas and content. When it's all in place it is just one more tool to encourage sales. As any other form of advertising, by itself it should not be relied on but to compliment your company, it's invaluable.
Good luck with it, I hope you take the necessary steps to ensure your website stands out from the vast numbers of rubbish ones out there.
Nicky.