The RDP connections from the outside interface toward the inside are allowed with the help of a combination of the access-list command and the static command.
The RDP works on the Transmission Control Protocol (TCP) port number 3389. Therefore, it is necessary to allow the inbound connection on port 3389 and to map the public IP address to the real IP address of the server.
Complete these steps:
1) Configure these static commands on the PIX:
Static (inside, outside) Public_ip_address_of_server real_ip address_of_server
2) Or, configure these static commands if the outside IP address of the PIX must be used for the connection:
Static (inside, outside) tcp interface 3389 real_ip address_of_server 3389
3) Configure these access-list commands on the PIX:
Access-list Outside_in permit tcp any host Public_ip_address_of_server eq 3389
Access-group Outside_in in interface outside