The information comes from two separate areas:
1. RunMRU entry in the registry. This can be cleared by editing the
registry, or by clearing the Recent documents list in the Start Menu and
Taskbar Properties.
Display, Use, and Clear "My Recent Documents" on the Start Menu in Windows
XP
http://support.microsoft.com/?kbid=307875
2. The entries that appear when you type something (but not normally
displayed when you click the drop-down), comes from the Index.dat (Internet
Explorer's) file. Clearing the Index.dat should help.
See MVP Mike Burgess' page:
http://www.mvps.org/winhelp2002/delcache.htm
-or-
Uncheck Use Autocomplete for "Web addresses" in IE Options Content tab
(AutoComplete settings dialog). FYI, unchecking this option, disables the
CTRL + ENTER (autosuggest) functionality in Intenret Explorer.