IE7 looks cool, but I do not recommend using it on your main machine. Since Firefox does not work well on some sites I use all the time, IE 7 had to go. It is not obvious how to remove it, but is documented in Microsoft's IE 7 Beta 2 FAQ:
How do I uninstall the preview?
To uninstall Internet Explorer 7 Beta 2
Preview and return to Internet Explorer 6 on Windows XP
- Click “Start,” and then click “Control Panel.”
- Click “Add or Remove Programs.”
- Check “Show Updates” at the top of the dialog box.
- Scroll down the list to “Windows XP – Software Updates,” select “Internet Explorer 7 Beta 2Preview,” and then click "Change/Remove."