Něco jsem vygooglil (je to pro BETu 2, ale snad ten správný odinstalační soubor najdeš)):


2. Run the commandline

%windir%\$NtUninstallie7b2pmx$\spuninst\spuninst.e xe

[%windir%\$NtUninstallie7bet2p$\spuninst\spuninst.e xe (according to the
dated Release Notes)]

Replace %windir% (above) with the path to your Windows folder, most often
'C:\Windows'. Make sure Show Hidden File and Folders is enabled via Control
Panel > Folder Options.

or

3. Go to the key

HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer

Right click on Internet Explorer > New String Value > Name that value
InstalledByUser (the value of the new String should be your User Account
name) > Uninstall IE7 via Add/Remove Programs.

Some software (for example CCleaner) deletes uninstaller directories such as
$NtUninstallie7bet2pmx$. If the $NtUninstallie7bet2pmx$ folder is empty, or
has been deleted completely, whether by third party software or manually to
preserve disk space, you will *not* be able to remove the Beta 2 Preview via
Add/Remove Programs or the commandline. If running System Restore does not
resolve the situation for you, then your only choice is to stay with the
Preview, or format your PC and install Windows anew. You will not be able
to install any future builds of IE7 while Beta 2 Preview is installed, nor
will you be able to run a Repair Install of XP.


Také jsem našel hardcore způsob takový, kde smažeš obsah složky Internet explorer v Program files a necháš opravit windows z instalačního CD (akorát pak musíš znovu instalovat updaty). Prý je to funkční. Můžeš to zkusit na vlastní riziko.