HW VSP adds a virtual serial port (COM5) to the system and redirects all communication over TCP/IP to remote IP address. HW VSP is free in unlimited version, it supports Windows 2000 and XP. HW VSP works with any TCP/IP device, it can work as a TCP server as well as a TCP Client. HW VSP supports remote RS232 port control (speed, parity, stop bits, etc..) over the RFC2217 (NVT). More virtual COMs can be created when launched with parameters.
Software that can be used as an alternative to HW VSP: