Tonight I was working on getting an Arduino accessible via TCP/IP using serproxy on Windows 7 64bit. I got it to the point where I can connect to my pc via telnet using the port in the serproxy.cfg file and get output from the Arduino.
I used a copy from tinkerit on google code in the comments by lanj... The modified source code can be downloaded from Alejandro Valenzuela Roca's blog.
Initially I had a the problem described on the comments where I could connect via telnet to the port and get output once but after that I would get 'Failed to open comm port - Connection refused' errors. The fix was to change the _close statement in sio.c in the sio_close routine to CloseHandle.
To compile serproxy I used CodeBlocks and imported the serproxy.dsp project file. After doing this and making the above change I was able to recompile it and successfully connect to the Arduino multiple times.
I tested successfully using both COM5 and COM14.