Johnathan,
Unless I'm mistaken, The SiliconDust HDHomeRun is not an officially supported
XP/MCE 2005 tuner, which would probably explain the error message you get
during setup.
I searched the MS knowledge base for a list of "Designed for XP/Media Center
2005" hardware. But, it appears that it's no longer posted on their website.
I have also read quite a few posts here on TGB from people who have "hacked" their
system registry in order to get HDHR to work with Media Center, but once again,
this seems to be a no-go for XP/MCE 2005 as the posts were by people using VMC.
I wish I could be more helpful to you, but at least this will solve the mystery of why it
doesn't install properly
BTW, in most cases, whatever tuner you do install for use with WMC will require you
to install a WMC specific driver and uninstall any/all standalone software & drivers that
might already be running or installed.
-Steve