rundll32 usually shows up when you invoke something from windows, for example like services window or i don't know, mouse settings window (but it can be something else too, this is just one common thing)
try ctrl-alt deleting rundll32 and see what happens
also, type msconfig, then click "run" tab and see what else may bring rundll32 up
but if you want to remove something you better do it other way, let me know if you want to
also, get
this wonderful tool and see what actually calls that rundll32