2 weeks ago my server was hacked and i have decided to install a Firewall to protect my system.
I hate to be hacked another time and I need to increase security.
I have Plesk 7 Reloaded in my server. But i need to understand the list of ports that I need to have opened in the firewall, for my system Plesk 7 Reloaded, to work.
Please provide me with the list of ports that I need to have opened in the firewall for my system to work (Plesk 7 Reloaded).

My suggestion here woudl be to only open the ports you need for the services you run...so start by running:

netstat -anp (as root of course)

to get a list of the ports that you are actually using at this point...and close/shutoff any you are not using. I would also recommend that you block 3306 (even though it is running)..as you really don't want outside mysql access