My 2 cents on installing IE7 (or ANY new software, registry hacks, etc.) BACKUP YOUR SYSTEM FIRST! I use Norton Ghost to create an image file of my entire C drive, including the registry, and I store the image files on an external hard drive. Once you have a backup you are free to experiment to your heart's content. You are even free to infect your system with nasty viruses. When something bad happens all you do is retrieve the last image file and all your mistakes are rolled back to the point where your computer was working perfectly. I installed IE7 Beta about a month ago, didn't like it, and removed it by going back to the image file I created just before installing IE7. The entire process took about 11 minutes and I have over 7GB of data on my C drive.
Happy tweaking,
Mark