True, it's not always easy to tell from what is displayed on the Startup tab of "System Configuration Utility" (run, MSCONFIG). Here is what I do in Windows 98: I clear every checkbox EXCEPT ScanRegistry, TaskMonitor, SystemTray, and (usually) LoadPowerProfile.
Then, if during the course of running my machine, I find something missing or disabled that I need, I look through the list of unchecked boxes and pick the most likely one. If that doesn't work, I'll try another one. The most cryptic names that I've found have been placed there by programs that are reminding you to register them.
I'd recommend you start off by reselecting the anti-virus files, but they only have to be loaded once, and you may not need every one of them (depending on the options you want).