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

  1. Click “Start,” and then click “Control Panel.”
  2. Click “Add or Remove Programs.”
  3. Check “Show Updates” at the top of the dialog box.
  4. Scroll down the list to “Windows XP – Software Updates,” select “Internet Explorer 7 Beta 2Preview,” and then click "Change/Remove."
If "Internet Explorer 7 Beta 2 Preview" does not exist, run %windir%$NtUninstallie7bet2p$spuninstspuninst.exe. You need to have "view hidden folders" enabled. %windir% is your Windows installation directory, which is normally 'C:Windows' on most systems.