Sub Domains and multiple Forums.

[Vgamer]

I am Curious if it is possible to segrigate forums. What i mean buy this is if i have multiple sub domains and i want lets say 5 categorys per sub domain but i only want those 5 categorys and the forums in them to show up for that sub domain even on the pop up list can this be done. The reason i ask is that i want to alow the same user name over multipe sub domain forums but i dont want ones sub domains categorys to be seen while in another.