you can try tell mirc to use this proxy to connect.
alt+o,connect,firewall, choose :
firewall support :server
protocol : proxy
hostname : ip of the proxy
userid, password : leave empty if your proxy don't request a username/passowrd to use it
port : enter your proxy port
some servers won't allow you to connect if they detect you're using a proxy or if there is any problem with ident protocol due to the proxy
