Digging into the dark recesses of my memory, I seem to recall that when you install IE you are asked if you wish to keep uninstall information. Anyway, this uninstall information is vital to restoring your prior version of IE. Without it you are, to use a technical term, screwed.
Now, you may very at some point delete this uninstall information, or may not have chosen to save it in the first place. Furthermore various system cleaning utilities and indeed Windows' own disk cleanup utility may delete these files to save space.
So, figure out if you've got the uninstall info and if you have, you should be able to go back. If not, you will probably not be successful.
Those systemworks type utilities (Norton and Ontrack) have a "go back" type utility but this only works well if you take a snapshot of your system before installing new software.