For the site I am working on, every Opportunity is a Quote. It is their sales method.

So if they are to make use of the Opportunity features, pipeline and graphs, they need to create the quote, cost up various products, then basically duplicate some info from the quote header in the Opportunity tab.

One way I can see to get around this would be to attach a trigger to the quote table that pushes data into the opportunity SPs on quote add/update/delete.