Also by your wording it implies you want the Quote number to drive the Opportunity number. In fact you would want the Opportunity number to drive the Quote number. This is because you can have Opportunities without a Quote, but Quotes must be linked to an Opportunity. 

Otherwise I agree with the others, what is the end result you're after and then we probably have an answer to that. 

Thanks for your replies

What I would like is to create an opportunity, from then on that opportunity number becomes the quote number

The problem at the moment is that we have an opportunity number and a quote number that are different

That's fine but you will have to customise the functionality to do that.  You will have to create a script to update the quote reference when you create a new quote.

That's fine but you will have to customise the functionality to do that.  You will have to create a script to update the quote reference when you create a new quote.