|I'd verify the port opens on the remote site - can you telnet (or nc) to port 3390 from your remote connection & the TCP connection opens or no?|
If no then it's got to be a routing issue on A if the NAT gateway works ok. You could verify that by installing Ethereal/Wireshark and looking for 'port 3389' traffic in the capture filter - verify the RDC packets are actually coming INTO A and weather or not they leave A on the other interface.
Sorry I don't know much about how ICS is routing any of this traffic - I've never used it personally. But if you do the above, it would at least prove the problem lies w/ ICS (or at node A).
If you can't get the secondary RDC forwarding going - my workaround would be to install cygwin, then install the SSH server: http://lifehacker.com/205090/geek-t...
After SSH is installed on A you can tunnel traffic through it using PuTTY. Localhost port 3390, remote: B's ip address:3389 - then you can RDC to localhost:3390 and traffic is tunneled through SSH. This is more of a linux solution though - cygwin makes the whole thing work on Windows, heh. That'd be my workaround if ICS won't cooperate.