Not sure what's happening here. I can reproduce this crash on a pristine XP2 SP2 pc - nothing on it except IE7 and Opus 9.0.0.7. The crash happens whether opus is running or not, or whether its replacing explorer or not.
I can make my car crash, I suspect it might be Opus-related. Eg, if I'm driving along, and suddenly swerve into a tree, it crashes. It definitely never did this before I had Opus installed.
Apart from the desktop double-click hook, Opus doesn't really get involved with the Desktop so it's unlikely to be the cause of the problem. The best thing to do is find someone with the same OS who doesn't have Opus installed and see if they still get the crash.
Internet Explorer does get involved with the Desktop rendering, especially with web content, so it could be a bug in IE7 on XP, perhaps?
The only machine I have that doesn't have Opus is running Vista so I can't help.