I'm trying to install IE6 on Windows XP, but the notification says that
"The installation is impossible as an updated version of IE is found on the computer".
Can I install IE6 without uninstalling the updated version?
No, you can only have one version installed. Note there are workarounds to do this, but nothing official. There are some tools to help test by using the various engines.
Plus later versions of IE allow you (in dev tools) to specify IE version.