I decided to take one of my old desktop towers and use it as a media center with my TV. I haven't touched the thing in probably 3 years, but when I went to Windows Update to check for some (ok probably a lot of) updates, it scans for awhile and then an error comes up that says it cannot display the page. Right before this I upgraded to IE7, and have noticed that certain pages will also come up with a cannot display error (particularly the netflix sign-in screen). These pages ARE accessible if I use Mozilla, though.

Is this a problem with WU, or IE7?

This is probably an IE security level setting.

Go to Tools > Internet Options > Security tab

Also, it could include a Privacy tab issue (next to the Security tab).

See that's what I though, so I checked the SSL settings in the security options and made sure all the SSL and TSL boxes were checked...but that didn't do anything. I've lowered the security down to medium, turned off all my security software...and it doesn't help.

I'm going to do a bit more digging...this is frustrating.

Give this a try...
download and install this program (it's free) CCleaner ... Alternative Download.
1. After installing...run the program...
Before the first use, select Options > Advanced and UNCHECK "Only delete files in Windows Temp folder older than 48 hours"
Click on Analyzer...then click on Run Cleaner.
2. On the left side of the window, click on Registry...click on Scan for issues...click on Fix selected issues.

This program will cleanup your temp files and cookies.

Nope, still not working.

I also updated reregistered all the XML and WU stuff, deleted the WU Temp folder, deleted McAfee (in case there was a security conflict)...I don't get it.

What URLs can you not display?

Try this ..
http://www.microsoft.com/downloads/d...displaylang=en

Just viewing it, or installing it? I can see that just fine, but the update is apparently "incompatible with the files of my system"

So far https://www.netflix.com/Login is the only site that consistently refuses to work. Gmail doesn't work either (but if I remember right, there's a different reason for that).

I finally tracked down the error description associated with the error code on the WU page.

"SEC_E_SECPKG_NOT_FOUND"

???