Mod Permissions in XF are different to how they work in VB. In VB you assign a mod to a forum, in XF any user you assign to be a mod is a mod everywhere, unless you set it up differently.
How you do this depends on how you want to do it. You can assign every mod's permission seperately if you wish, or if you have number of moderator groups - i.e. some people responsible for Forums A, B and C, another group responsible for Forum D, E and F and another few looking after G, H and I; you would create 3 moderator groups, set mod permissions for Forums A, B and C for Mod Group 1, D,E and F for Mod Group 2 and G, H and I for Mod Group 3.
Then whichever user you added Mod Group1 as a secondary group they would be able to moderate the Forums in Group 1. Likewise, assign Mod Group 2 to anyone you want to moderate forums D, E and F.
Unless you have a specific need though, I'd just let moderators moderate everywhere. We started out on our forum with mods specific to certain areas of the forums, but it just worked better for us for any mod online having the power to perform moderator actions anywhere on the forum - it saved members having to wait until the mod responsible for the particular area coming online to do whatever needed to be done.
But if you wanted to allocate moderators per area you can set it up as per the guidelines above.