Guys, after a period of stability lasting almost a year (last encountering this problem in Oct of 2010) I find that the issue has reared it's ugly head again.
I tend to find it occuring (but not exclusively limited to) when I'm browsing the Internet, although also regularly occurs when I have iTunes playing.
I have attached the relevant, with the exception of the perfmon / report (I get an error message 'The Perameter is Incorrect').
Given the age of my System (almost 7 years old, and originally Windows Media Centre) I'm using the most recently available Drivers
(to my knowledge).
I look forward to some positive resposes.