Microsoft warns of SP3 IE7 lock-in
If you choose to install XP SP3, Internet Explorer 7 will remain on your system after the install is complete,” said Jane Maliouta, an IE program manager, in the blog entry. “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.”
The inability to downgrade to IE6 after installing XP SP3 was by design, said Maliouta, because the service pack includes newer versions of the old browser’s files. If Microsoft had allowed users to revert back to the pre-SP3 version of IE6 — the one saved on users’ PCs when they upgraded to IE7, and what was used until now to back out of the newer browser — Windows would have ended up in a “mixed file state,” Maliouta said.