I was having trouble with the extender, I tried EVERYTHING on MS's help page to no avail. I searched for a few hours and could not find anything.. That's why I am posting this..
My setup is...
Windows 7 Ultimate. Wired to router.
Xbox 360 wired to router.
Tried two routers. WRT54G running DD-WRT and Belkin 8236 4v1
No matter what ports I opened or what firewalls I shut down the extender just would not set-up.
Finally I called Microsoft and they told me to do this.
In this order!
-Start Menu > Services
-Internet Connection Sharing (ICS): Startup Type:Disabled, [Stop], [Apply], [Ok]
-Network List Service: Startup Type:Automatic, [Start], [Apply], [Ok]
-SSDP Discovery: Startup Type:Automatic, [Start], [Apply], [Ok]
-UPnP Device Host: Startup Type:Automatic, [Start], [Apply], [Ok]
-Media Center Extender Service: Startup Type:Automatic, [Apply] [Start], [Apply], [Ok] (This one I don't know why but I had to hit apply for the automatic start before I could start it, The MS guy said that's common.)
-Right Click SSDP Discovery>Restart
-Try to connect the extender again.
The MS guy said that for some reason Windows 7 Ultimate comes with media center but the extender is disabled.. So this is what you need to do to fix it..
Best of luck.. Worked for me.