I have no solution to this, but the same thing happens with my laptop, also running Windows Vista Home Premium. Your description is very clear. When I look to the top of the screen it says ".....Internet Explorere provided by Dell (Not Responding)". It lasts for a few seconds then resumes as normal.
It seems to happen almost every time I return to the machine after a period of time when the screen saver has been running. Bloody annoying.
I seem to remember it did not happen so often before I installed Skype a few weeks ago. Maybe that has something to do with it.