|Ok, I know it's silly to pick nits but nomenclature actually IS important.|
I doubt very much you're using a hub. Most likely it's a switch. If you're not sure check and in the future, let's call a hand a hand and not a foot....doing that just leads to confusion.
From what I see, you have the following setup:
Internet >> SOHO Router >> Switch >> Server/Clients
Is this correct?
If it is, and your clients aren't able to contact the DC check your DHCP and ensure they're getting the IP of your DC (192.168.2.50) as their DNS address
You can open a command prompt window on a client and type:
to confirm if they're getting the correct DNS address. If they're not, then you know what your problem is and you have to enter the correct one in your DHCP scope.
You will also need to forward the DNS on your DC to your ISP's DNS server(s).
This way your DC's DNS will resolve all queries inside the local zone and will pass along all external queries to your ISP's DNS server(s).