I have 2 currency rate installed (C1, C2), and i have many product categories in my store
what i need is to display some categories price with (C1), and the other categories with (C2)
how can i do this
By default you won't be able (and maybe you shouldn't because is confusing).
Maybe you can use a second price attribute as reference but quote and cart will work with only 1 currency at time.