By simply un-installing IE your pc should automatically revert to the earlier version, you do not need to re-download or install the earlier version. At least, that is how it works with XP, I do not have Vista so cannot advise if that will work the same way.
To uninstall Internet Explorer, go to Control Panel, and click on Uninstall Programs link or Programs and Features icon. Then on Tasks pane on the left, click on View installed updates link. Locate and select Windows Internet Explorer in the list of installed updates, and then click on Uninstall button. Click on Yes when asked that are you sure want to uninstall the update.