NotC: This is for the Beta releases ( 7.0.5346.5 + ) not the pre-beta releases

When you try to install Microsoft Internet Explorer 7 beta 2, the installation wizard finishes, but the last screen displays the following error messagC:

Internet Explorer 7 could not be installed. You must restart your system to confirm that any changes to your system are undone.
After restarting, follow the "Internet Explorer Troubleshooting" shortcut on your desktop to get more information.

Step 1) Go to the Microsoft page http://support.microsoft.com/kb/917925 and follow the directions there.  If you do not locate the errors they specify on that page then go on to step 2.

Step 2) Restart your computer.  Run the setup program again but this time follow the directions.  Close ALL running applications including your anti-virus program and anything else that is showing in the area near the clock.  One of the setup pages will tell you to do this.  That is your last chance and if you don't do it then the install will probably mess up again.

Contrary to the note at the top of the page, Step 2 does apply to the pre-beta releases and most other installations.

Also just as a tip,  I unchecked both items on the optional installs page.  In particular I wanted to avoid Defender.  That is still in Beta and running two betas together does not seem like a good idea.  You can have enough problems with one.