Help! Remove/Prevent unwanted crap.

WIN98SE NS &/orIE
How can I prevent files being installed without my permission? I already fight the cookie battle by not allowing any that aren't personally approved. Granted, I'm not the only user, but is there a way to have the computer ask permission to install stuff?
Here are a few examples that 'just appreared' on the StartUp list:

AutoUpdater in C:\WINDOWS\SYSTEM\aupdate.exe

PornKings Download Plus in C:\WINDOWS\APPLIC~1\DOWNLO~1.EXE

EnsoniqMixer (its there twice) in
starter.exe

rb32lptto1 in
"c:\program files\rb32\rb32.exe" (with quotes)

How do I get rid of this stuff, get them off the StartUp list, prevent them from getting there in the first place?

Thanks a lot.