do this (assuming your in win2k)
set the history settings to how you want them (100 days or something)
click the start button, then click run
type mmc and hit enter
click on the console menu, then click add/remove snap-in
click the add button
add the group policy option.
click ok on the add/remove snap-in box
now click on the user configuration option, then administrative templates, then internet explorer
the option you want to change is the disable history settings - enable that
now people cant clear the history