Well, one correction here. While this happens in the Slide Show and Simple Slide Show visualizations, it does not happen as I had thought in G-Force (3.01). What I am seeing there is that cover art larger than the program's 200x200 default size for cover art is not being resized to fit 200x200, but rather showing a blank frame where the resized cover art should appear. However, I guess I will have to write off using the Slide Show visualizations on the Windows XP platform.
I've seen other messages on the Net of similar problems. Apparently MS invented ActiveX and then decided it is too dangerous to allow its customers to use, even when the ActiveX is installed on and running on the local computer. Way to go, Bill.
And even though the message box is from Internet Explorer, there doesn't seem to be any way to set the Security there low enough or in a way that affects what's going on in Media Center. I've even tried adding my local computer on the Trusted Sites tab (192.168.x.x., \\computer\drivec, etc.), but to no avail.