Most of the problems I found on the Internet dealing with this problem mentioned having older versions of I.E. (like 4.0 or 5.0).
I will look some more, but I recommend you look too (double the bandwidth!), and you better understand your setup.
Did you ever install the Beta version of IE7?
There were some XP updates that broke some people, but again, you'll probably need to look at these.
I googled
mk:@MSITStorebut you might start by googling
chm error 