It really depends on a number of variables. How many and what type of interfaces do you have on the 7500? What about your 6500s? How do these devices (7500 and 6500s)connect to the rest of your network? How large is the rest of your network? I think it would be difficult to generalize for you how to connect this gear together without understanding what you have and what you want to do.
I would be easy to say connect all of the .com gear to one of the 6500s and all of the .net gear to the other. Connect both switches to difference interfaces on the 7500 and create your ACLs there to prevent network to network communication. It is rarely that easy in the real world, though.