Ok this may sound a little far fetched, but do you have Windows Media Player10? I've heard that helped, & I certainly downloaded & installed it myself; also & this is probably the strangest solution yet, changing from optical mouse to a standard rollerball.

If that fails pop to Totalwar.com & check their forums, you'll have to jump through a couple of post links, but there's a wealth of info. on different system issues & install / running problems.