ok, in win98 you should be able to do it by going through system information found under system tools, but i dont see why it is a huge deal for you, first off anyone that wants to hack you bad enough to wait for just the right moment between loading applications must really want something off of your hdd, and if they wanted it that bad they could surely get past your firewall, secondly, odds of anyone knowing when you are booting up, almost zip- so basically you really dont have anything to worry about at all.
Just my 2 cents
Jak