diff -Naur meld-1.1.5/meldapp.py meld-1.1.5-dbus/meldapp.py
--- meld-1.1.5/meldapp.py	2007-06-09 19:29:28.000000000 +0200
+++ meld-1.1.5-dbus/meldapp.py	2007-07-26 11:46:09.000000000 +0200
@@ -34,6 +34,23 @@
 import task
 
 # optional
+# dbus
+dbus_available = 0
+try:
+    import dbus
+    import dbus.service
+    if getattr(dbus, 'version', (0,0,0)) >= (0,41,0):
+        import dbus.glib
+        dbus_available = 1
+    else:
+        pass # dbus version too old
+except ImportError:
+    pass
+    # FIXME: Do I print this error or give the silent treatement?
+    #print "Oops, no dbus. Please install the python-dbus package."
+    #print "Meld will not be able to launch new diffs in existing window."
+
+# sourceview
 sourceview_available = 0
 
 for sourceview in "gtksourceview sourceview".split():
@@ -814,9 +831,34 @@
             [(gtk.STOCK_QUIT, gtk.RESPONSE_CANCEL), (gtk.STOCK_OK, gtk.RESPONSE_OK)] )
         if response == gtk.RESPONSE_CANCEL:
             sys.exit(0)
-        
-        
-        
+
+    def parseargs(self, args, label = []):
+        tab = None
+        if len(args) == 0:
+            pass
+
+        elif len(args) == 1:
+            a = args[0]
+            if os.path.isfile(a):
+                doc = vcview.VcView(self.prefs)
+                def cleanup():
+                    self.scheduler.remove_scheduler(doc.scheduler)
+                self.scheduler.add_task(cleanup)
+                self.scheduler.add_scheduler(doc.scheduler)
+                doc.set_location( os.path.dirname(a) )
+                doc.connect("create-diff", lambda obj,arg: self.append_diff(arg) )
+                doc.run_diff([a])
+            else:
+                tab = self.append_vcview( [a] )
+
+        elif len(args) in (2,3):
+            tab = self.append_diff(args)
+        else:
+            self.usage( _("Wrong number of arguments (Got %i)") % len(args))
+
+        if tab:
+            tab.set_labels( label )
+
 ################################################################################
 #
 # usage
@@ -828,6 +870,56 @@
 
 ################################################################################
 #
+# DBus stuff
+#
+# You either have dbus, or you don't.
+# If you don't, I can't help yah,
+# if you do, you either have meld running already or you don't.
+# 
+# If you don't, I'll register the meld dbus interface,
+# if you do, you either want a new window or not.
+# 
+# If you don't, I'll pass those args along the bus,
+# if you do, I'll just start a new window.
+#
+# -Kacper Wysocki (comotion@users.sf.net)
+#
+################################################################################
+
+class MeldDbus(dbus.service.Object):
+    def __init__(self, bus_name, app, object_path='/net/sf/meld'):
+        dbus.service.Object.__init__(self, bus_name, object_path)
+        self.app = app
+
+    @dbus.service.method('net.sf.meld')
+    def diff(self, args):
+        self.app.parseargs(args)
+
+def register_dbus(app):
+    session_bus = dbus.SessionBus()
+    bus_name = dbus.service.BusName('net.sf.meld', bus=session_bus)
+    remotemeld = MeldDbus(bus_name, app)
+
+def try_dbus():
+    bus = dbus.SessionBus()
+    proxy = bus.get_object('org.freedesktop.DBus',
+                           '/org/freedesktop/DBus')
+    iface = dbus.Interface(proxy, 'org.freedesktop.DBus')
+    names = iface.ListNames()
+    if "net.sf.meld" in names: # does meld dbus interface exist?
+        return 1 # Found a running instance, passed things along
+    return 0 # didn't 
+
+def pass_args_dbus(args):
+    bus = dbus.SessionBus()
+    proxy = bus.get_object('net.sf.meld','/net/sf/meld')
+    iface = dbus.Interface(proxy, 'net.sf.meld')
+    iface.diff(args)
+
+
+
+################################################################################
+#
 # Main
 #
 ################################################################################
@@ -842,7 +934,6 @@
         def __getattr__(self, attr):
             return getattr(self.file, attr)
     sys.stdout = Unbuffered(sys.stdout)
-
     parser = optparse.OptionParser(
     usage="""
     %prog                       Start with no windows open
@@ -853,38 +944,25 @@
     description="""Meld is a file and directory comparison tool.""",
     version="%prog "+version)
     parser.add_option("-L", "--label", action="append", default=[], help=_("Set label to use instead of file name"))
+    parser.add_option("-n", "--new-window", action="store_true", dest="force_window", help=_("Open new window regardless"))
     parser.add_option("-u", "--unified", action="store_true", help=_("Ignored for compatibility"))
     parser.add_option("-c", "--context", action="store_true", help=_("Ignored for compatibility"))
     parser.add_option("-e", "--ed", action="store_true", help=_("Ignored for compatibility"))
     parser.add_option("-r", "--recursive", action="store_true", help=_("Ignored for compatibility"))
     options, args = parser.parse_args()
 
+    running_already = 0
+    if dbus_available:
+        running_already = try_dbus()
+        if running_already:
+            if args and not options.force_window:
+                pass_args_dbus(args)
+                return
+    # either you're forcing a new window or it ain't running yet
     app = MeldApp()
-    tab = None
-
-    if len(args) == 0:
-        pass
-
-    elif len(args) == 1:
-        a = args[0]
-        if os.path.isfile(a):
-            doc = vcview.VcView(app.prefs)
-            def cleanup():
-                app.scheduler.remove_scheduler(doc.scheduler)
-            app.scheduler.add_task(cleanup)
-            app.scheduler.add_scheduler(doc.scheduler)
-            doc.set_location( os.path.dirname(a) )
-            doc.connect("create-diff", lambda obj,arg: app.append_diff(arg) )
-            doc.run_diff([a])
-        else:
-            tab = app.append_vcview( [a] )
-                
-    elif len(args) in (2,3):
-        tab = app.append_diff(args)
-    else:
-        app.usage( _("Wrong number of arguments (Got %i)") % len(args))
+    if dbus_available and not running_already:
+        register_dbus(app)
 
-    if tab:
-        tab.set_labels( options.label )
+    app.parseargs(args, options.label)
     app.main()