Index: twisted/internet/interfaces.py
===================================================================
--- twisted/internet/interfaces.py	(revision 29075)
+++ twisted/internet/interfaces.py	(working copy)
@@ -408,6 +408,37 @@
         """
 
 
+
+class IReactorWin32Events(Interface):
+    """
+    Win32 Event API methods
+    """
+    
+    def addEvent(event, fd, action):
+        """
+        Add a new win32 event to the event loop.
+
+        @param event: a Win32 event object created using win32event.CreateEvent()
+
+        @param fd: an instance of L{twisted.internet.abstract.FileDescriptor}
+
+        @param action: a string that is a method name of the fd instance.
+                       This method is called in response to the event.
+
+        @return: None
+        """
+
+    def removeEvent(event):
+        """
+        Remove an event.
+
+        @param event: a Win32 event object added using L{IReactorWin32Events.addEvent}
+
+        @return: None
+        """
+
+
+
 class IReactorUDP(Interface):
     """
     UDP socket methods.
Index: twisted/internet/win32eventreactor.py
===================================================================
--- twisted/internet/win32eventreactor.py	(revision 29075)
+++ twisted/internet/win32eventreactor.py	(working copy)
@@ -1,12 +1,18 @@
-# Copyright (c) 2001-2007 Twisted Matrix Laboratories.
+# Copyright (c) 2001-2010 Twisted Matrix Laboratories.
 # See LICENSE for details.
 
 
 """
 A win32event based implementation of the Twisted main loop.
 
-This requires win32all or ActivePython to be installed.
+This requires pywin32 (formerly win32all) or ActivePython to be installed.
 
+To install the event loop (and you should do this before any connections,
+listeners or connectors are added)::
+
+    from twisted.internet import win32eventreactor
+    win32eventreactor.install()
+
 Maintainer: Itamar Shtull-Trauring
 
 
@@ -58,6 +64,7 @@
 from twisted.internet import posixbase
 from twisted.python import log, threadable, failure
 from twisted.internet.interfaces import IReactorFDSet, IReactorProcess
+from twisted.internet.interfaces import IReactorWin32Events
 
 from twisted.internet._dumbwin32proc import Process
 
@@ -76,7 +83,7 @@
     @ivar _events: A dictionary mapping win32 event object to tuples of
         L{FileDescriptor} instances and event masks.
     """
-    implements(IReactorFDSet, IReactorProcess)
+    implements(IReactorFDSet, IReactorProcess, IReactorWin32Events)
 
     dummyEvent = CreateEvent(None, 0, 0, None)
 
Index: twisted/internet/test/test_win32eventreactor.py
===================================================================
--- twisted/internet/test/test_win32eventreactor.py	(revision 0)
+++ twisted/internet/test/test_win32eventreactor.py	(revision 0)
@@ -0,0 +1,23 @@
+# Copyright (c) 2010 Twisted Matrix Laboratories.
+# See LICENSE for details.
+
+"""
+Tests for L{twisted.internet.win32eventreactor} and supporting code.
+"""
+
+from twisted.trial import unittest
+from twisted.internet import reactor
+from twisted.internet.interfaces import IReactorWin32Events
+
+from zope.interface.verify import verifyObject
+
+class win32eventreactorTestCase(unittest.TestCase):
+    """IReactorWin32Events"""
+
+    def test_provides_interface(self):
+        verifyObject(IReactorWin32Events, reactor)
+
+
+
+if reactor.__class__.__name__ != 'Win32Reactor':
+    win32eventreactorTestCase.skip = 'This test only applies to win32eventreactor'

Index: twisted/internet/_win32serialport.py
===================================================================
--- twisted/internet/_win32serialport.py	(revision 29075)
+++ twisted/internet/_win32serialport.py	(working copy)
@@ -21,6 +21,7 @@
 from twisted.protocols import basic
 from twisted.internet import abstract
 from twisted.python import log
+from twisted.internet.interfaces import IReactorWin32Events
 
 # sibling imports
 from serialport import BaseSerialPort
@@ -34,6 +35,12 @@
     def __init__(self, protocol, deviceNameOrPortNumber, reactor, 
         baudrate = 9600, bytesize = EIGHTBITS, parity = PARITY_NONE,
         stopbits = STOPBITS_ONE, xonxoff = 0, rtscts = 0):
+
+        if not IReactorWin32Events.providedBy(reactor):
+            raise ValueError(
+                "SerialPort on Windows requires a reactor that "
+                "implements IReactorWin32Events, e.g. win32eventreactor.")
+        
         self._serial = serial.Serial(deviceNameOrPortNumber, baudrate=baudrate,
                                      bytesize=bytesize, parity=parity,
                                      stopbits=stopbits, timeout=None,
@@ -52,7 +59,7 @@
         self._overlappedRead.hEvent = win32event.CreateEvent(None, 1, 0, None)
         self._overlappedWrite = win32file.OVERLAPPED()
         self._overlappedWrite.hEvent = win32event.CreateEvent(None, 0, 0, None)
-        
+
         self.reactor.addEvent(self._overlappedRead.hEvent, self, 'serialReadEvent')
         self.reactor.addEvent(self._overlappedWrite.hEvent, self, 'serialWriteEvent')
 
Index: twisted/internet/serialport.py
===================================================================
--- twisted/internet/serialport.py	(revision 29075)
+++ twisted/internet/serialport.py	(working copy)
@@ -4,6 +4,15 @@
 
 """
 Serial Port Protocol
+
+pySerial is required for all platforms: http://pyserial.sourceforge.net/
+
+Windows requires the use of a reactor that supports
+L{twisted.internet.interfaces.IReactorWin32Events}
+e.g. L{twisted.internet.win32eventreactor}
+
+pywin32 (previously win32all) is also required for Windows:
+http://sourceforge.net/projects/pywin32/
 """
 
 # http://twistedmatrix.com/trac/ticket/3725#comment:24