Also VERY interested in a plugin/script.
I know this may be a real challenge - there is only one way to capture to file directly from slingbox (that I have head of..)
Sort of does screen scrapping so the resolution and quality sort of sucks (your PC beeps and that is captured too)
Hint - as in last posting - flash based from sling.com might be the best approach.
I am not a programmer but have a sling box pro and would be willing to test if anyone comes up with something.
Keep me on your list...