First off you need to understand that IE8 is native to Windows 7 - That is 7 ships with IE8 installed (US Versions)
Also when you messed with those registry keys for IE you pretty much hosed the system. In that instance you would be better served to do a Repair install as suggested by A Guy and Hopalong.
My two cents.
Thanks for the tip but I ended up reinstalling W7. Things got a bit complicated when I installed Acronis OS Selector further on. So, I finally got rid of that product and am letting W7 handle the xp-W7 dual boot. Things are fine now with a clean slate.
But I still don't understand why it wouldn't let me install IE9 beta. Anyhow, I'm using Firefox to avoid those problems.
Once you've screwed up the IE install, in general you can't install a newer version because the previous version checks will fail. That is why you couldn't install IE9 beta - it didn't know if you had a previous version of IE it could upgrade properly.
I only got rid of all registry entries referring to IE because, from the start, it wouldn't accept the upgrade. All I had originally done was to inadvertently delete the IE application module. Everything else was still around.
As you've learned, that is not the way to get rid of IE as it can, and did, wreck your system. Take it as a lesson learned.
Peace
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