I'm running ver 2.7 and added the serial library from source forge. here is the error I get:

Traceback (most recent call last):
  File "C:\Python27\Lib\site-packages\pythonwin\pywin\framework\scriptutils.py", line 326, in RunScript
    exec codeObject in __main__.__dict__
  File "C:\Documents and Settings\Administrator\My Documents\WTF.py", line 3, in <module>
    import serial
ImportError: No module named serial

here is my code:
# Echo client program
import socket
import serial

HOST = '216.240.155.229'    # The remote host
PORT = 9090              # The same port as used by the server
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect((HOST, PORT))
ser = serial.Serial('USB0', timeout=3)
x = 0
#while x < 5:
while True:
    msg = ser.readline()
    s.send(msg)
    x += 1
s.close()

This bug tracker is for reporting CPython bugs, so it's not the right place where to ask this kind of questions.
Anyway make sure that the "serial" module is in a directory that Python can see, e.g. the same dir where you have your script.