If you can't uninstall the old IE7 for any reason, try the following:

Remove from the registry:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\Curr entVersion\Uninstall\ie7b2pmx

and

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Updates\Wind ows XP\SP0\ie7b2pmx

Then, replace your iexplore file (C:\Program Files\Internet Explorer\iexplore.exe) with the iexplore.exe from Internet Explorer 6.

Now when you run the IE7 installer again, it should pass its "checks" to see if you have IE7 already installed and let you install again.