Finally got a chance to look at a Shuttle on XP, not the same as an Extreme.
VLC seems to sort of work with it.. but with a lot of trouble.
The Decklink device drivers reject a 720x486 or 720x488 resolution and default to something ridiculous like 720x30.
But trying the Blackmagic WDM driver seems to behave ok with 720x480, but doesn't provide an audio stream.. so right now its very confusing.
The Blackmagic Desktop Video and Driver suite on Windows XP is the first version that I know of that included support for both XP and Thunderbolt Shuttle.. so I guess its a bit early and unstable.
Noel AMCap seems to work just fine with it, and Blackmagic Media Express, and GraphEdit seems to work with it.