What programs do I really need? Which are SpyWare?

I continue to find many SpyWare applications when I run
AdAware. I remove these files, but find other files in my
system that I don't recognize and I don't know if I even
need them. Should I delete files I don't recognize? What
do I need? In particular, System32 and WINNT files: what
are these? Can i delete them?

thanks