Do renewals have a different record type/layout than initial opportunities? If so, then you may need to set the record type BEFORE the new (blank) Opportunity is created. This would require overriding the New Opportunity page with an interim page that will count ClosedWon Opportunities for that Account (or whatever criteria you need) and will do a different redirect based on the count.
However, if you have the identical record type and you just want to show if there are existing C/W Opps for that Account, then do the Roll-up Summary field and a formula on Opportunity that will show a different image if the RUS is 0 or >0.
However (yeah, I make it so complicated) if there can be multiple initials and renewals for each Account going at the same time (a company may have multiple concurrent contracts for something) then you'll probably need to put a lookup from the renewal to the original opportunity... and the RUS won't work at all - you'll need a trigger before insert/update on Opportunity to fill the right values and such on the Opportunity record.