Within the Opportunities module I have a 'Stage' field that tells me how far through the sales process each opportunity is (prospect, qualified, proposal, verbal agreement, closed won etc) 

I want to be able to run a report on the number of opportunities that move to a 'proposal' stage each week, and also the number of opportunities at the 'proposal' stage that move to 'closed won'. 

Is this possible? 

Using the 'Modified Time' criteria isn't sufficient, as it reports on any modification. I need to specify the field that is modified and what it has been modified to. 

Thanks for your help.