Low System Resources Problem

When I boot up my system resources stand at 70% after I run anything it gets
down into the low 60's eventhough I closed the application. As it gets lower
the system gets slow and eventually hangs. I have a PIII-600 with 256meg ram.
I don't do anything fancy, just small spreadsheets or word documents. I did
notice that my firewall 'Zone Alarm 4' is a real pig and uses up 13% of my
resources. Is there a better product that uses less resources. How do I find
out what the offending applications are and how do I turn off some of these
things from being memory resident. I am not a techy which is why I am looking
for the help.

Many thanks in advance.
Bob