diff --git a/Lib/os.py b/Lib/os.py
index bb90f2eed59..dda32135669 100644
--- a/Lib/os.py
+++ b/Lib/os.py
@@ -7,6 +7,8 @@
 # - os.curdir is a string representing the current directory ('.' or ':')
 # - os.pardir is a string representing the parent directory ('..' or '::')
 # - os.sep is the (or a most common) pathname separator ('/' or ':')
+# - os.pathsep is the component separator used in $PATH etc
+# - os.defpath is the default search path for executables
 
 # Programs that import and use 'os' stand a better chance of being
 # portable between different platforms.  Of course, they must then
@@ -14,40 +16,29 @@
 # and opendir), and leave all pathname manipulation to os.path
 # (e.g., split and join).
 
-# XXX This is incorrect if the import *path fails...
+_osindex = {
+	  'posix': ('.', '..', '/', ':', ':/bin:/usr/bin'),
+	  'dos':   ('.', '..', '\\', ';', '.;C:\\bin'),
+	  'nt':    ('.', '..', '\\', ';', '.;C:\\bin'),
+	  'mac':   (':', '::', ':', ' ', ':'),
+}
 
-try:
-	from posix import *
-	try:
-		from posix import _exit
-	except ImportError:
-		pass
-	name = 'posix'
-	curdir = '.'
-	pardir = '..'
-	sep = '/'
-	import posixpath
-	path = posixpath
-	del posixpath
-except ImportError:
-	try:
-		from mac import *
-		name = 'mac'
-		curdir = ':'
-		pardir = '::'
-		sep = ':'
-		import macpath
-		path = macpath
-		del macpath
-	except ImportError:
-		from dos import *
-		name = 'dos'
-		curdir = '.'		# XXX doesn't always work
-		pardir = '..'		# XXX doesn't always work
-		sep = '/'		# XXX or '\\' ???
-		import dospath
-		path = dospath
-		del dospath
+import sys
+for name in _osindex.keys():
+	if name in sys.builtin_module_names:
+		curdir, pardir, sep, pathsep, defpath = _osindex[name]
+		exec 'from %s import *' % name
+		exec 'import %spath' % name
+		exec 'path = %spath' % name
+		exec 'del %spath' % name
+		try:
+			exec 'from %s import _exit' % name
+		except ImportError:
+			pass
+		break
+else:
+	del name
+	raise ImportError, 'no os specific module found'
 
 def execl(file, *args):
 	execv(file, args)
@@ -59,22 +50,49 @@ def execle(file, *args):
 def execlp(file, *args):
 	execvp(file, args)
 
+_notfound = None
 def execvp(file, args):
-	if '/' in file:
+	global _notfound
+	head, tail = path.split(file)
+	if head:
 		execv(file, args)
 		return
 	ENOENT = 2
 	if environ.has_key('PATH'):
-		import string
-		PATH = string.splitfields(environ['PATH'], ':')
+		envpath = environ['PATH']
 	else:
-		PATH = ['', '/bin', '/usr/bin']
-	exc, arg = (ENOENT, 'No such file or directory')
+		envpath = defpath
+	import string
+	PATH = string.splitfields(envpath, pathsep)
+	if not _notfound:
+		import tempfile
+		# Exec a file that is guaranteed not to exist
+		try: execv(tempfile.mktemp(), ())
+		except error, _notfound: pass
+	exc, arg = error, _notfound
 	for dir in PATH:
 		fullname = path.join(dir, file)
 		try:
 			execv(fullname, args)
 		except error, (errno, msg):
-			if errno != ENOENT:
+			if errno != arg[0]:
 				exc, arg = error, (errno, msg)
 	raise exc, arg
+
+# Provide listdir for Windows NT that doesn't have it built in
+if name == 'nt':
+	try:
+		_tmp = listdir
+		del _tmp
+	except NameError:
+		def listdir(name):
+			if path.ismount(name):
+				list = ['.']
+			else:
+				list = ['.', '..']
+			f = popen('dir/l/b ' + name, 'r')
+			line = f.readline()
+			while line:
+				list.append(line[:-1])
+				line = f.readline()
+			return list