FYI, for anyone who can't get doubleTwist on their computer to find their device when attempting to sync for the first time. Assuming you have the proper access, go into your router settings and disable anything that says "block multicast" or "filter multicast" or something to that affect. In some cases, your router might have the option to turn multicast on/off. Whatever the configuration, you want multicast to be unrestricted.
Once you've done that, see if doubleTwist will sync with your phone.
I found the solution in a thread on the doubleTwist forum (they are attempting to troubleshoot the issue with several users posting the same problem over there). Disabling the "filter multicast" worked like a charm for me.
Now, all is well!
Hope this helps.
-SR-
PS: I wonder if this is the same reason I couldn't get Winamp to find my device either. Hmmmm...