As I said in an earlier post, I'm fairly sure I was not having this problem when I first installed 10.6.4 (or any other Apple update). It was only a few days ago that I first noticed Hulu Desktop getting interrupted with the screensaver (the night following the start of this topic, to be precise), but I installed 10.6.4 on the day it was released, June 16th, almost two weeks ago.
I am almost certain that several time in the following week I watched programs without touching mouse, keyboard, or IR remote for at least as long as my screensaver was set to startup & never saw that happen.
I don't know if this means Hulu did something in the last few days or I changed something on my iMac during the same period, or what. I think I still have a clone of my system I made just prior to applying the 10.6.4 update, so if I can find the time to make sure I still have it & test with it, I may be able to learn more. If so, I'll post what I find out.