Windows XP SP3 and IE7 - The unistallation puzzle

Case 1 : You have IE7 on XP SP2. Install XP SP3 on top of it.  You wil not be able to unistall IE7 and revert to IE6 unless you un-install XPSP3.

Case 2. : You have IE6 on XP SP2. Install XP SP3. Then install IE7. If this configuration is followed IE7 can be unistalled and reverted to IE6 with out uninstalling SP3.

Below is an excerpt from IE Blog:

" If you choose to install XPSP3, Internet Explorer 7 will remain on your system after the install is complete. Your preferences will be retained. However, you will no longer be able to uninstall IE7. If you go to Control Panel->Add/Remove Programs, the Remove option will be grayed out.

This behavior is by design and here is why. When we install IE7 on Windows XP SP2, we backup the existing IE6 files in an uninstall directory.  Those IE6 files are the ones that shipped on XPSP2 plus all the security updates you’ve installed while using IE6. Windows XP SP3 contains a newer version of the Internet Explorer 6 files. If you have XPSP3 on your system and uninstall IE7, your system would revert to the backed up (older) version of the IE6 files rather than the newer XPSP3 version. You would end up in a mixed file state in Windows where most files would be the upgraded XPSP3, except for the IE6 files restored when uninstalling IE7. This state is not supported and is very bug prone. To ensure a reliable user experience, we prevent this broken state by disabling the ability to uninstall Internet Explorer 7.

If you must uninstall IE7 after you have upgraded to XPSP3, then you have to first uninstall XPSP3, and then uninstall IE7. After this series of uninstalls, you will be reverted back to a XPSP2, and a stable version of IE6, so feel free to upgrade to XPSP3 again.

If you install IE7 after you install XPSP3, then you will be able to uninstall IE7 at any point and be reverted to the newer IE6 version that ships in XPSP3. The restriction on uninstalling only applies to when you install a Windows Service Pack release on top of a standalone IE release.

Keeping this in mind, you might want to uninstall IE7, upgrade to XPSP3 and then install IE7 again so you can uninstall IE7 in the future if need be."

http://blogs.msdn.com/ie/archive/2008/05/05/ie-and-xpsp3.aspx