diff --git a/twander.py b/twander.py
index 1520cd9..1ecb298 100755
--- a/twander.py
+++ b/twander.py
@@ -4,7 +4,7 @@
 
 
 PROGNAME = "twander"
-RCSID = "$Id: twander.py,v 1.22 2002/10/30 00:00:23 tundra Exp $"
+RCSID = "$Id: twander.py,v 1.23 2002/10/30 23:28:35 tundra Exp $"
 VERSION = RCSID.split()[2]
 
 
@@ -81,9 +81,11 @@
 #####
 
 eBADROOT = " %s Is Not A Directory"
+eDIRRD   = " Problem Reading Directory : %s"
 eDUPKEY  = "Duplicate Key In Configuration File Found In Entry: \'%s\'"
 eERROR   = "ERROR"
 eNOCONF  = "Cannot Find Configuration File: %s"
+eNOENV   = "Configuration File References Undefined Environment Variable: %s"
 eOPEN    = "Cannot Open File: %s"
 eTOOMANY = "You Can Only Specify One Starting Directory."
 
@@ -128,8 +130,9 @@
 
 MainApp   = gui.Application()
 MainWin   = gui.Window(height=300,
-                       width=500
+                       width=500,
                        )
+
 DirList   = gui.ListBox()
 MainWin.add(DirList,
             hstretch=1,
@@ -166,13 +169,16 @@
 def BuildDirList(rootdir):
 
     dList, fList = [], []
-
-    dList.append("..")
-    for file in os.listdir(rootdir):
-        if os.path.isdir(os.path.join(rootdir,file)):
-            dList.append(DIR_LDELIM + file + DIR_RDELIM)
-        else:
-            fList.append(file)
+    dList.append(DIR_LDELIM + ".." + DIR_RDELIM)  # Always show one directory up
+    
+    try:
+        for file in os.listdir(rootdir):
+            if os.path.isdir(os.path.join(rootdir,file)):
+                dList.append(DIR_LDELIM + file + DIR_RDELIM)
+            else:
+                fList.append(file)
+    except:
+        ErrMsg(eDIRRD % rootdir)
 
     dList.sort()
     fList.sort()
@@ -182,6 +188,52 @@
 
 
 #####
+# Event Handler For Directory Listing ListBox
+#####
+
+def DirList_Handler(**kwargs):
+    global rootdir
+    selected =  DirList.items[DirList._get_selection()]
+
+    # If selection is a directory, move there and list contents.
+    # We examine this by checking the string for the directory
+    # delimiter characters previously inserted in BuildDirList()
+    
+    if selected[0] == DIR_LDELIM and selected[-1] == DIR_RDELIM:
+        # Strip off delimiters to get real name
+        selected = selected[1:-1]
+
+        # Build full path name
+        selected = os.path.join(os.path.abspath(rootdir), selected)
+
+        # Convert ending ".." into canonical path
+        if selected.endswith(".."):
+            selected = PSEP.join(selected.split(PSEP)[:-2])
+        
+        # Need to end the directory string with a path
+        # separator character so that subsequent navigation
+        # will work when we hit the root directory of the file
+        # system.  In the case of Unix, this means that
+        # if we ended up at the root directory, we'll just
+        # get "/".  In the case of Win32, we will get
+        # "DRIVE:/".
+
+        selected += PSEP
+
+        # Save the new root location and get its contents
+        rootdir = selected
+        DirList.items = BuildDirList(rootdir)
+
+        # Update main window to reflect new location
+        MainWin.set(title= PROGNAME + " " + VERSION + "        " + rootdir)
+
+    else:
+        print("Not a DIR!")
+
+# End of 'DirList_Handler()
+
+    
+#####
 # Print An Error Message
 #####
 
@@ -224,7 +276,12 @@
 
                 # Process environment variables
                 if fields[x][0] == ENVIRO:
-                    fields[x] = os.getenv(fields[x][1:])
+                    envval = os.getenv(fields[x][1:])
+                    if not envval:       # Environment variable not defined
+                        ErrMsg(eNOENV % fields[x])
+                        sys.exit(1)
+                    else:
+                        fields[x] = envval
 
             # Get command key value and store in dictionary
 
@@ -239,7 +296,7 @@
             else:
                 key = fields[0][keypos+1]   # Use selected key as index
 
-            if key in rcfile:
+            if key in rcfile:               # This is a Python 2.2 or later idiom
                 ErrMsg(eDUPKEY % fields[0]) # Duplicate key found
                 cf.close()
                 sys.exit(1)
@@ -328,9 +385,19 @@
 rcfile = {}
 ParseRC()
 
-# Fill the control with directory contents
+# Canonicalize the rootdir
+rootdir = os.path.abspath(rootdir)
+
+# Initialize ListBox with info for starting directory
 DirList.items = BuildDirList(rootdir)
 
-MainWin.set(title= PROGNAME + " " + VERSION + "    -     Examining:    " + rootdir)
+# Initialize the title for the main window
+MainWin.set(title= PROGNAME + " " + VERSION + "       " + rootdir)
+
+
+# Link ListBox handler
+gui.link(DirList, DirList_Handler)
+
+
 MainApp.run()