It's a while since I used ME and IE5.5, but I do remember having a similar problem with the auto complete and also parental controls.
Even uninstalling IE had no effect.
If you are familiar with the registry you can turn off the function within the registry and also delete the autocompletes that have been "saved". That may help, but only do it if you are confident....
In the end I gave up and got IE6 and XP. No problems since then and of course XP will allow separate profiles for each user.