Which processes can I end?

An aquaintance told me to close unnecessary programs and end processes that
are running needlessly to help with performance. I usually have about 56
processes running after startup. Is that a lot? Most seem to be part of the
system or network services. The rest are inflicted by me the user, I gather,
from add ons, etc. How can I tell which I can end at any given time to help
performance but keep necessary ones running?
Running Vista home on a Celeron M in a Toshiba laptop about two years old.
Trend PC-illin provides security. Any tips welcome.
Jim in Milwaukee