Windows: how to downgrade Internet Explorer 8 to an older version?

"seems nobody know about Comptability View feature in IE8, its was specialy designed to correct such issues you may have with old entreprise web-applications or such. you don't have to downgrade.

Internet Explorer 8 is a new release
and some websites may not yet be ready
for the new browser. Click the
Compatibility View toolbar button to
display the website as viewed in
Internet Explorer 7, which will
correct display problems like
misaligned text, images, or text
boxes. This option is on a per site
basis and all other sites will
continue to display with Internet
Explorer 8 functionality. When you
click on the Compatibility View button
for a site, you don’t need to do it
again as the next time you visit that
site the browser will show it in
compatibility mode. If for some reason
you’d like to go back to browsing with
Internet Explorer 8 functionality on
that site, simply click the
Compatibility View button again.

more info at msdn.com"

Try this: How do I uninstall or remove Internet Explorer 8?. It's a microsoft support article. If you installed ie 8 prior to XP sp3 you're out of luck and can't remove it. If you cannot get it to uninstall you can try installing another copy of windows into a virtual machine and use IE 7 from there.