
There are so many variations on what a breeder may wish from you as a co-owner that it's impossible to cover them all ;-) As others have said there may be future issues that have nothing to do with your enjoyment of showing such as breeding terms etc. Even just from a show point of view, the breeder's expectations (or yours of the breeder) could be totally in conflict - even over feeding, coat care and general condition before you get to perhaps simply not wanting to travel to certain shows etc.
If you really want to show, do a lot of research on the breed, attend some shows and chat to exhibitors, contact the breed club and get list of available litters and get acquainted with those you may be interested in getting a show puppy from. Then, when something suitable is available, buy the puppy outright and your carefully chosen breeder should be more than happy to assist in any way with getting you started in showing. That way if circumstances change in the future and you can't or don't want to continue with the hobby it is only your own feelings that need be taken into consideration.
Personally, I would not co-own a dog - mine are always pets first and foremost so it's only what suits our family that dictates what we do with them. Just my opinion of course - but hope whatever you decide works out :-)
Teri