Outlook Express

I have uninstalled Outlook Express, Ver.6. from my HD.  I use Courier 3.5 as my default mail program,(Password protected). In Tools, Internet Options, Programs, E-mail, the drop down window has OLEXP listed as a choice. How can I remove that choice? Even with OLEXP uninstalled, it will still open and reveal messages that comes into my POP account on my ISP. if someone clicks to make it the default. If It cant be removed, how can a password be applied so it will have to be entered each time before it will open when the Mail Button is pressed. This is a shared computer.

Thanks,           IE6.0, Win 98se