Slow Computer?, Use this troubleshooting checklist
Have you done the things suggested in the above topic?
When did the slowdown start? Before or after you installed Zone Alarm? I ask because there is no one size fits all when it comes to computer security. What works for me may not work for you.
It is possible that Zone Alarm doesn't play nice with your computer.
Do you have a desktop? If so, have you ever opened up the case and cleaned the dust out of the PC innards?
Try the simple things first, if those don't work, post back and let us know so more suggestions can be made.