Simplest possible gstreamer networking test, from a batch file:
gst-launch-0.10 audiotestsrc ! udpsink host=192.168.1.100 port=23000
A quick glance with Wireshark reveals that no packets are being sent (a "full" test with transmitter and receiver also shows no network communications happening).
Windows 7, with firewall turned off. Same result in Windows XP.