Quartus II 7.2 & Declaring bus range problem

I don't see a problem. When you create a symbol file for your VHDL component, the generics are automaticly used as block parameters, you can show them in the schematic. You can change the parameter value in the schematic according to your needs, either use a fixed value or a global parameter as in my below example that simply instantiates the gray_counter from Quartus VHDL templates.