Sorry you're having a tough time with this Tom. Sounds like a pain in the patootie!
Unfortunately, IE8 being in test phase (beta) has nothing to do with how your WindowBlinds is acting.
If WindowBlinds was working correctly with IE7, then it's a beta issue with your new browser. And Microsoft doesn't support beta products.
Again it's unfortunate, but these are the risks of being a beta tester. And you're laying your system down on the line in the name of developement. I love testing, but I passed on this one because IE7 isn't broken.
Revert your browser back to IE7, clean your registry of any remnants of IE8, makes sure all of your service packs are up to date and see if this clears it up. As a last resort, roll your system back to before you installed IE8.
If IE8 is treating your system like crap, pass on the testing and wait for the full version to launch. Soon as the bugs are knocked out, I'll be there too.
Good Luck Tom!