Can you give me a few more details on your network setup? How is the Tivo connecting to your PC, wirelessly, hard-wired? Are you able to see the Tivo on your network? For example I have a wireless router that when I go into the control panel of it I can see everything connected to my home network, both wireless and ethernet connections.
I just finished wiring the rooms with our Tivos with gigabit ethernet wiring for a few reasons. I found the wireless connection could get flaky at times with the Tivo, and HD video took forever to transfer. Even though the Tivo only has a 10/100 ethernet plug in the back I went gigabit for any other device that can use 10/100/1000. It is amazing the difference in transfer times. A 30 min program recorded in standard def can transfer between machines or the PC in about 2-3 mins. HD video goes about 5-8 mins, it has enough of a head start that there are no lagging issues when I try to watch the program immediately.
A few things you may check on the Tivo Desktop software: For some strange reason I never understood the wireless always seemed to be a bit more reliable when using the "Tivo Beacon" setting vs. Bonjour. Also I always went and manually selected all the Tivo boxes to be part of the shared network vs. letting it auto detect.