Just a heads-up for everyone, I found that accessing *live* feeds from BBC iplayer via ISA-2006 or TMG-2010 resulted in Internet Explorer hangs every 5 minutes or so. Had to restart IE to recover internet access.
I Googled-around but couldn't find a fix, but after some analysis of the TMG logs, the cause became apparent: Flood Mitigation is intervening. Solution: under ISA/TMG flood mitigation, raise the MAXIMUM HTTP REQUESTS PER MINUTE PER IP ADDRESS setting from 600 to 3000.