Over the next few years gaming will continue to rely more and more on broadband; Cisco's forte. Nintendo already has a powerful application in Nintendo Wi-Fi, a wireless network used in conjunction with the Nintendo DS and the to-be-released Nintendo Revolution.
So, what would happen if Nintendo were to be purchased by Cisco? From the consumer's point of view, I doubt that they would see much difference. Nintendo already has it's plans for both software and hardware. Plans that have proven to be very effective (look at Nintendogs, for example). I doubt that Cisco would want to mess with their strategy.
Instead, Nintendo would have a vast amount of resources with which to work. Not only would they have more cash for developing games and hardware, but they'd have a direct line into a huge broadband network.
In all honesty, I doubt that Nintendo would go for such a deal. They seem too proud to let something like that happen.