Just a note in case someone else is struggling with this. All of a sudden my extender stopped connecting to my Media Center PC last night for no apparent reason. Something about a 00020002 error. After troubleshooting it for a while I finally noticed from the event log that the conflict was with the Beta Microsoft Windows AntiSpyware application I had installed the day before. I removed the AntiSpyware product and it started working again.
This Extender discussion forum on thegreenbutton looks like it may be handy to read from time to time. Someone else was having the same problem and apparently has already contacted Microsoft about it.
I've spoken to two people who own Media Center Extenders who weren't aware that there is an update available from Microsoft for both the Linksys and the HP extenders. For me it significantly improved the stability of my Linksys WMCE54AG extender. I haven't had one lockup since I installed it, and it no longer cuts the last couple of seconds off of songs I am playing. Just thought I'd post the link to the update in case any of you happen to be running extenders at home.